Yes, Apple is playing the long game. And, as Steve said back in 2005, there is a building somewhere on Apple's campus where Mac OS Ax has been leading a secret double life.
And, yes, every app in Apple's pocket has been optimized—or is being optimized—for Mac OS Ax. This is already all running in the labs, or the sky is yellow!
And also, yes, Adobe and Microsoft are very well positioned to meet this next transition head-on, as most of their suites are already running on ARM. If they aren't seeing the writing on the wall, then they aren't very bright.
In fact, with MS having a lot of code already working on ARM, it may not be very long after Apple goes all in that the PC industry starts playing more than just part time. Intel should be scrambling right now, and if they aren't then they aren't very bright either.
And, if Apple does use the iMac as the jumping-off point, well, that would be pretty crazy. But I don't think that's the case. I think they start with a laptop in the MacBook range.