Pre-emptive apology for longpost - not all of it is aimed at you!
This is the first time I've seen Tumblr mentioned in overarching discussion of "what are we going to do about Facebook and Twitter?" that HN (and others) have been having recently.
OP's two main concerns about Twitter both stem from the fact that it's a centralized system belonging to one company:
1) It's a single point of failure; everything is lost if Twitter goes bankrupt.
2) Twitter holds and (more visibly, recently) is exercising supreme veto power over who gets to use their product and what they use it for. (Note: opinions diverge here; some think Twitter isn't effective enough at identifying and curtailing abuse; others think Twitter is censoring free speech. Both are possible because of centralization, both are bad.)
Tumblr is still centralized and thus solves neither of these concerns, but you are aware of that; you cited it as a possible model, not as a drop-in solution. But real, federated blogging already exists - OP is using Wordpress, not Blogspot, Ghost, etc. (Hey, you can even self host Wordpress! or Jekyll, Hexo, etc.)
As discussed elsewhere in this thread, basic tools exist for federated blog networking and discovery - RSS, blog rolls, search engines. Like OP, I think there is significant margin for improvement in the UX of those tools.
Tumblr's barrier to entry is almost nil - username, password, bam - but WP's free hosted option honestly isn't far behind. That kind of setup would work for average users. If it had good network/discovery tooling built into the platform using open standards, it'd be on par with Tumblr.
But on top of that, a user banned from free WP hosting has the option of buying shared hosting pre-installed with WP from another provider and still being able to participate. It goes down a continuum of ease-of-setup vs. degree of control through VPS to a machine in the basement.
"But why would you want people who get banned that much to still be able to publish?" People get bullied off Tumblr not infrequently through malicious mass reporting. The automatic thresholds are not that hard to trip; the people that suffer are the ones that have developed a following but are not "famous".
I've seen a webcomic artist disappear from Tumblr because they drew a panel of character A calling character B a virgin insultingly. A fan discussion developed over whether B was canon asexual. The artist contributed and said they weren't. This set off a whole bloc of users who started calling the artist heteronormative and a lot of other things, and they eventually mass reported the artist's accounts and got them banned.
Of course there are support channels to rectify this sort of thing, but the process, from what I've seen, is usually painful and slow and not guaranteed to be successful. If the artist gets their account(s) back (which the one in my story did), they now publish in fear of offending that one portion of their fandom, which both dampens their motivation to publish (usually not high for internet artists) and can result in work that panders to the disruptive fans, to the displeasure of the others who were enjoying the artist's original work. If the artist doesn't get their account back (refused by staff or too much trouble), they often lose irreplaceable artwork and history (though shame on them for not doing local backups). If they choose to open a new account, they have have to rebuild their fandom from scratch and PMs to whoever they have non-Tumblr connections with, or they will be found by the troublemakers again and basically be in the same situation as if the account was reopened except still missing all the archives. If both seem like too much trouble, they fold and are never heard from again.
Anyway, this kind of thing has happened to too many people that I was interested in who used Tumblr, which is what, three or so? Enough that it seems like a problem.
- - - -
This is somewhat of an aside, but the design choices Tumblr has made that make it more than a simple blogging platform have strongly colored its community.
I found a blogpost titled "The Toxoplasmosa of Rage"[0] a while back that mused at length about why and how people get so mad about the things they do, especially now that we have the Internet facilitating it. Tumblr was only one of many subjects he touched on, but it stuck with me the most. Put succinctly: on Tumblr, you don't comment on posts; you reblog them and add your own commentary. Both post and commentary are seen by the previous (re)blogger(s) and your followers, who often share your views.
The result is that if material is only seen by people who like it, everyone is happy - but if (as frequently happens) someone sees something they don't like and are compelled to comment on it, Tumblr's system sets up a perfect storm of vitriol as material is alternately bounced between clusters of the network with opposing opinions.
All of which now seems especially ironic to me, given the recent uptick of interest in more accurately identifying echo chambers in media (social and otherwise), and attempting to negate them somehow, possibly by adjusting feed algorithms to expose people to opposing ideas more often. Damned if you do, damned if you don't.
It's worth noting that the traditional blog platform avoids this issue by keeping comments confined to the post they were made on.
There are some systems that fuzzy the system so it isn't totally compartmentalized. Disqus is its own little network, for instance. I think Wordpress uses its own commenting ecosystem so people can click on the profile pic of your comment and find your blog, if you have one. Backlinking also increases connectivity by letting readers know who has responded to the piece they're reading, which I hardly consider a bad thing. Maybe the context shifts forced by systems like backlinking or comment linking dampen fly-off-the-handle emotional reactions that fuel flame wars like on Tumblr or Twitter. HN does something similar by hiding the reply link from the front page when a chain nests deep enough, forcing you to go to the comment's own page to reply. Just a little kick, asking "is replying really necessary?".
This is the first time I've seen Tumblr mentioned in overarching discussion of "what are we going to do about Facebook and Twitter?" that HN (and others) have been having recently.
OP's two main concerns about Twitter both stem from the fact that it's a centralized system belonging to one company:
1) It's a single point of failure; everything is lost if Twitter goes bankrupt.
2) Twitter holds and (more visibly, recently) is exercising supreme veto power over who gets to use their product and what they use it for. (Note: opinions diverge here; some think Twitter isn't effective enough at identifying and curtailing abuse; others think Twitter is censoring free speech. Both are possible because of centralization, both are bad.)
Tumblr is still centralized and thus solves neither of these concerns, but you are aware of that; you cited it as a possible model, not as a drop-in solution. But real, federated blogging already exists - OP is using Wordpress, not Blogspot, Ghost, etc. (Hey, you can even self host Wordpress! or Jekyll, Hexo, etc.)
As discussed elsewhere in this thread, basic tools exist for federated blog networking and discovery - RSS, blog rolls, search engines. Like OP, I think there is significant margin for improvement in the UX of those tools.
Tumblr's barrier to entry is almost nil - username, password, bam - but WP's free hosted option honestly isn't far behind. That kind of setup would work for average users. If it had good network/discovery tooling built into the platform using open standards, it'd be on par with Tumblr.
But on top of that, a user banned from free WP hosting has the option of buying shared hosting pre-installed with WP from another provider and still being able to participate. It goes down a continuum of ease-of-setup vs. degree of control through VPS to a machine in the basement.
"But why would you want people who get banned that much to still be able to publish?" People get bullied off Tumblr not infrequently through malicious mass reporting. The automatic thresholds are not that hard to trip; the people that suffer are the ones that have developed a following but are not "famous".
I've seen a webcomic artist disappear from Tumblr because they drew a panel of character A calling character B a virgin insultingly. A fan discussion developed over whether B was canon asexual. The artist contributed and said they weren't. This set off a whole bloc of users who started calling the artist heteronormative and a lot of other things, and they eventually mass reported the artist's accounts and got them banned.
Of course there are support channels to rectify this sort of thing, but the process, from what I've seen, is usually painful and slow and not guaranteed to be successful. If the artist gets their account(s) back (which the one in my story did), they now publish in fear of offending that one portion of their fandom, which both dampens their motivation to publish (usually not high for internet artists) and can result in work that panders to the disruptive fans, to the displeasure of the others who were enjoying the artist's original work. If the artist doesn't get their account back (refused by staff or too much trouble), they often lose irreplaceable artwork and history (though shame on them for not doing local backups). If they choose to open a new account, they have have to rebuild their fandom from scratch and PMs to whoever they have non-Tumblr connections with, or they will be found by the troublemakers again and basically be in the same situation as if the account was reopened except still missing all the archives. If both seem like too much trouble, they fold and are never heard from again.
Anyway, this kind of thing has happened to too many people that I was interested in who used Tumblr, which is what, three or so? Enough that it seems like a problem.
- - - -
This is somewhat of an aside, but the design choices Tumblr has made that make it more than a simple blogging platform have strongly colored its community.
I found a blogpost titled "The Toxoplasmosa of Rage"[0] a while back that mused at length about why and how people get so mad about the things they do, especially now that we have the Internet facilitating it. Tumblr was only one of many subjects he touched on, but it stuck with me the most. Put succinctly: on Tumblr, you don't comment on posts; you reblog them and add your own commentary. Both post and commentary are seen by the previous (re)blogger(s) and your followers, who often share your views.
The result is that if material is only seen by people who like it, everyone is happy - but if (as frequently happens) someone sees something they don't like and are compelled to comment on it, Tumblr's system sets up a perfect storm of vitriol as material is alternately bounced between clusters of the network with opposing opinions.
All of which now seems especially ironic to me, given the recent uptick of interest in more accurately identifying echo chambers in media (social and otherwise), and attempting to negate them somehow, possibly by adjusting feed algorithms to expose people to opposing ideas more often. Damned if you do, damned if you don't.
It's worth noting that the traditional blog platform avoids this issue by keeping comments confined to the post they were made on.
There are some systems that fuzzy the system so it isn't totally compartmentalized. Disqus is its own little network, for instance. I think Wordpress uses its own commenting ecosystem so people can click on the profile pic of your comment and find your blog, if you have one. Backlinking also increases connectivity by letting readers know who has responded to the piece they're reading, which I hardly consider a bad thing. Maybe the context shifts forced by systems like backlinking or comment linking dampen fly-off-the-handle emotional reactions that fuel flame wars like on Tumblr or Twitter. HN does something similar by hiding the reply link from the front page when a chain nests deep enough, forcing you to go to the comment's own page to reply. Just a little kick, asking "is replying really necessary?".
[0]: http://slatestarcodex.com/2014/12/17/the-toxoplasma-of-rage/ (CTRL-F for "completely different" if you only want Section V that mentions Tumblr)