Part of what you say could be forced by similar situation as with Longhorn/Vista & various stuff - with the store using tech not available on win7, the best course (resource-wise) is to try to get everyone to update to 10. The problem here is that even if the update is free from 7, there's so much changes and the net experience isn't clearly positive - it just makes more sense to wait as long as possible hoping that a future version gets things together.
I could see third party bringing as much of the 7 UI experience to 10 as possible and that might be good enough for those on the fence. I just don't like the idea of replacing even more of the shell and control panel with 3rd party stuff as that stuff is the most prone for compat issues and serviceability/security patching is potential issue as well. And business users probably don't like the implementation either while the idea* might seem sound. (*of turning 10 taskbar,start menu, control panel into not much different than 7)