"Perhaps, as has happened in the PC space, Apple will be content to make a healthy profit as a high-value, high-cost niche player while Android supports more and more variants offered by more and more manufacturers."
There's no 'perhaps': this is *exactly* what Apple wants. It's where the best margins are.
Google don't give a damn who uses Android, so long as they get their ad revenues (and license fees), so they'll very likely do very well in the mid- and low-end markets. No matter what happens, they'll "win", because they'll make their money regardless of the actual sale price of the devices. Their entire strategy has been to ensure that the only *guaranteed* profits in the Android market go to Google.
WinPho7 *might* be a contender. Microsoft have at least *tried* to do something different. Unfortunately, so did the Jupiter Ace, so this isn't a guarantee. Nevertheless, Microsoft's offering offers some genuine innovation in the GUI field, while Android does not.
I expect MeeGo to become the Linux of the smartphone world: we'll see it pop up its head here and there, but it's unlikely to get much traction inside the core smartphone market. (I expect to see it more often in STBs and other consumer electronics as there's little to choose from between it and Android: both are just Linux variants with different plastic surgeons.) It's unlikely to catch up with Android unless Google do something seriously stupid.
Or I could be completely and utterly wrong.