Microsoft is somewhat similar to Google in the sense that the OS and eco-system is all the company builds. hardware is delegated to the partners. this is usually the case with Microsoft. they make money from licensing the operating system.

would MS allow Qt to run on WP7? unlikely. what business sense is there in this? this requires investment from MS to open up APIs that would allow Qt to work. unless Nokia can show this, they get the boot. so my guess is, Nokia will start working with building a sizeable market for WP7 on Nokia hardware (much the same like what HTC did many moons ago) and then go back to MS and have a business case for the next step.

there was a joke internally in Microsoft's MCB division years back. people joked about Microsoft working with Nokia to build Windows Mobile phones. and MS said that they would LOVE to work with Nokia but the reverse was unlikely to be true. oh how times have changed!