There is one thing that would get me to upgrade from my 7D to a potential 7D Mark II: A massively improved sensor.
To be more specific: Better noise performance and dynamic range.
Even at very low ISO settings, skies can sometimes be slightly grainy and there's almost no information to pull out of the shadows. And what makes it even worse is that this is an area, where older Canon APS-C sensors were actually better at.
I don't care about the resolution of the sensor, as long as the image quality improvements are there. If they aren't, I'll happily keep my current 7D because overall, it's still an awesome camera.
Actually, I'm sometimes surprised at how well some of the high-ISO pictures turn out (I've had some great keepers which were shot at ISO5000), but of course any improvement here would be highly welcome as well.
Another thing I'd love to have would be an adjustable minimum shutter speed, but I think it's pretty safe to assume that it will be there (at least in the same way the 5D3 supports it).