I'm curious if MS continues to test other major UI design changes internally, or if they're basically now stuck on old style (menus, mainly) vs. ribbon, casting ribbon as "the one true solution". Personally I'd also like to see some innovation aimed at power users, for example more powerful context menu functionality. Imagine context menus that can have more sophisticated visual elements, even encompassing things like pie/circle menu functionality, etc. Granted your average user isn't going to take to that like shoving buttons in their face, which is more an issue of using the UI as a wedge to increase user *awareness*, it's not necessarily as effective at improving long-term efficiency once awareness exists, but as I said the power users deserve some dev time too.
In a sense power users might be more important for MS on the desktop given the move toward "appliance computing". MS might be best served looking at file maintenance, etc. as fundamentally power user features and focusing end-user-oriented research more on automation. A good example of a start on that would be defaulting to auto-sort downloaded movie files into the movie library, audio files into music, photos into photos. Sure power users would hate that, but I'd bet average users would love it. And if MS could create a Gmail-esque "tag or don't as you please, search will take care of everything anyway" system (think Everything but properly integrated in the OS), then eventually I reckon the power users would come around too. But regardless I feel like power users get short shrift on MS innovations and that may be driving people away from MS's desktop OS's long term toward e.g. Linux. Or not, given Linux desktop adoption percentages.
Anyway I'm not a fan of the ribbon UI and annoyed to see MS continuing to push it. I just hope they leave it as optional and not just an option to minimize it, but an option to have the same UI we have now. Then again there are always 3rd party file managers...