That’s exactly what we are using jsonnet for at my company. Introducing jsonnet in our CloudFormation work has given great results with almost zero up front cost (compare with other CloudFormation DSLs). This reminds me I should finish writing that blog post about it :)
Do you use pass-phrases with your per-host keys? I wanted to do this, but was unable to make it manageable. ssh-agent will only try so many keys before moving on.
If you mean how have I used it specifically, I've used it to do a variety of things. Ranging from recreating what was described in the original post to using it as an ad hoc MPI replacement. I find it's handy for managing jobs that have some coupling (and so aren't easily suited to running via the features of the batch system), but aren't tightly coupled enough to warrant the suffering of having to write MPI-based code.
FIFY
As the user, I fully trust my Epiphany browser.