Another thought: your point is valid, but they should use something other than qemu (e.g. they could probably just buy VMWare with their loose change), and make sure it is running x86 code, not arm. The ARM emulation is I believe the main source of the performance problems in the Android emulator, since it relies on software translation rather than hardware-assisted virtualisation. I've never understood why Google don't use x86 in their emulator, given that almost all Android apps are written in Java.

I think it would be a moderately difficult engineering task, but certainly not outside Apple's capabilities. Ultimately it's a question of whether or not Apple sees benefits in doing so, which I suspect they don't.

It's also interesting to note that back in the dying days of NeXT, when they realised they weren't going to make much money from hardware, they switched to a software-only approach and actually did a port of all the Cocoa frameworks to Windows NT, and you could write Cocoa applications and have them run on windows. So it's not impossible to do this, but given the amount of changes that have happened to the APIs since that time it would probably be easier to go down the VM route.