Will everyone run 7 well past its support lifecycle? Will Linux win the desktop? Will we get a new round of commercial OS competition? Will Windows 9 try to roll back to a more traditional desktop OS?
I think these questions will be determined by what businesses do, being the intractable giant footprint of desktop usage (with apologies to SteamOS).
Microsoft is offering extended support for XP, but at discouragement prices. 7 will probably be similar, so "just stick on 7 forever" is out.
Commercial OS competition seems an unlikely possibility. It'd be hard to attract new entrants when those currently best positioned to exploit the market are either near monopolies or free. It's too bad, more competition in the space would probably produce some really great ideas.
Big companies do learn from their mistakes, even after years of heading in the wrong direction. There's just so much inertia in capital. IBM and Apple have shown that you can coast for a long time on bad decisions then make a startling recovery. Sometimes this takes a massive cultural shift though, or visionary new leadership. It could happen, and probably will eventually. We're on a tight timeframe though, so I put the chances of that happening before Windows 9's release at only around 20%.
That only leaves the possibility that some Linux variant will take over, maybe one designed to really cater to small to medium sized business owners. MS Office probably keeps that from ever happening though. (And I can't feel that comfortable about any line of analysis that ends with, "Linux will take over the desktop.")
I've run out of options. Maybe 2015 will be the year of Android on the desktop.
EDIT: Or Apple, sure.