I'm not quite sure if you're saying that Apple may start selling the MacBook Air with some locked down iOS-like OS on them while leaving OS X on their other chunkier PCs, or if you're saying they're going to entirely get rid of OS X as we know it today. I think both scenarios are pretty unlikely, though the latter one would be most unlikely IMO. What would they expect people to develop iOS apps on if they fully lock down or take away OS X? The biggest single reason I switched to a Mac (about 5 years ago now) was because it was a reasonably well curated (in terms of the GUI) Unix machine with a lot of commercial support and I could employ the various *nix utilities that I was used to, having previously used a combination of Linux and Windows for my computing needs. If Apple no longer offered a full featured Unix based environment, they'd precipitate a mass developer exodus of which I would certainly be amongst. I believe such a move would be no less than the most egregious foot shooting of all time for any tech company ever.

But all this is not to say I don't have a Plan B if against all reason, Apple was to decide to enrage just about every developer that builds on their platforms... I would sigh somewhat heavily, shake my head in disbelief and then it would be back to Linux with a touch of Windows (and possibly Android) on the side. Not my first preference obviously, but not such a bad thing all in all.