I don't think that going to happen in the next twenty years or so. Remember there are 1.1 billion computers that run Microsoft operating system and it would take an insurmountable effort to erase the client OS and convert everything to the cloud.
Microsoft didn't want to alienate it's users because the Windows XP interface from Vista was a major change and large companies would need to mount massive training for their people. Today, Microsoft is just leveraging on the Vista look and feel to have simple move towards Windows 7.
I liked the menu in Vista a lot and the Windows 7 has taken it a step further. Nonetheless, I can live with either Vista or Windows 7, they are almost identical in a lot of ways.
I don't think so, as long as Windows 7 is as fast as Windows XP with the power of Windows Vista, Microsoft would have a powerful economic swing on Windows 7.