Apple does look like it's making chips to handle heavy workloads, not just to compete with the latest Krait or whatever. But I'm not sure ARM Macs are the direction they'll take that.
It'd make some business sense for them to instead position iOS so it can take over more and more traditional Mac duties. The IBM push could be an example of that. Investing in iOS gives Apple the tight control and the 30% cut they're used to from that space, and it avoids the Windows-RT-ish heartbreak of "why is this ARM OS like my Intel OS but without all my apps?" (If there were Mac-on-ARM, I'd expect it to be Mac App Store only.)
> why is this ARM OS like my Intel OS but without all my apps?
The problem should be much smaller on OS X than on Windows. Apple has a culture of breaking things regularly, instead of worshipping backwards compatabillity.
The result is that most Mac apps are kept up to date by the developer. Recompiling for an arm-based OS X shouldn't be an issue.
> The result is that most Mac apps are kept up to date by the developer.
That's maybe true for indie developers. It's not generally true for things like Photoshop, Microsoft Office, MATLAB, Mathematica, Skype, and dozens of other major titles that would likely be complete dealbreakers for a pretty significant portion of their userbase.
Apple kept Carbon (the OS9 to OS X transitional bindings) around for so long because of Photoshop and Office.
From personal experience, I can tell you that this does not happen with big software. Apple released the first Intel Macs in early 2006. The next year Intuit released Quicken 2007 which was PPC only.
The first version of Quicken to be x86 for Mac was Quicken Essentials 2010. First of all that's four years after the transition. Second, Quicken Essentials was crippled. Here's a quote from Wikipedia:
> Some of the features of Quicken are not present in Quicken Essentials for Mac, such as the ability to track investment buys and sells or to pay bills online from the application.
So unless you wanted something ultra-basic you were screwed. Intuit's answer was that they'd give you a free copy of Quick '08 for Windows. All you needed to do was buy Parallels (etc.) and Windows.
This was a big problem because OS X finally dropped PPC emulation support, called Rosetta, in 2011 with the release of Lion. So after 5 years Intuit, a VERY big company, was unwilling to update their software or provide a real equivalent for their Mac users.
If you look at the announcements for each version of Adobe Creative Suite for Mac you'll find references to starting to use features of the OS that Apple introduced years ago.
It'd make some business sense for them to instead position iOS so it can take over more and more traditional Mac duties. The IBM push could be an example of that. Investing in iOS gives Apple the tight control and the 30% cut they're used to from that space, and it avoids the Windows-RT-ish heartbreak of "why is this ARM OS like my Intel OS but without all my apps?" (If there were Mac-on-ARM, I'd expect it to be Mac App Store only.)
Anyway, the A7 is already a beast (http://www.anandtech.com/show/7910/apples-cyclone-microarchi... does various measurements, http://cryptomaths.com/2014/04/29/benchmarking-symmetric-cry... is an interesting case study), and there are still future process nodes and microarchitecture changes that will let them make better chips. I don't know if an ARM MacBook Air is specifically where this goes, but they're certainly making ARM capable of more serious stuff.