Whether I upgrade from my current 7D to the 7D II or to Fullframe mainly depends on:
1. Sensor quality
Needs to have minimum +2 EV Hi ISO AND DR .. atv ALL ISOs, including 100. in RAW. Do not care abaout ooc jpeg
Also, I am perfectly fine with with 18MP on APS-C, do not need 24.
2. AF system
the closer to 1D-X the more likely I will take it :-)
If it falls short on count 1 or 2. I will definitely not buy it.
At the rumoured price tag I would also expect:
* FULLY functional Auto-ISO - exactly like in Nikon D800
* Wifi, GPS built in - but not "always on"!
* Pop-Up flash with optical wireless commander - as in 7D
* additionally a built in Canon RT-radio transmitter .. that chip is probably only a few square millimeters. so fits easily alongside a pop up flash. It is not -... one or the other!
* fps .. I do not need 10 ... 8 is plenty for me, I would even accept 6 if IQ would be improved
* video .. don't ever use it, don't need it, don't want it. Buy a camcorder, canon makes nice ones.
IF I move to FF .. and Canon wants my money, it needs to be a 5D IV at the price of a Nikon D800, besting the Nikon's sensor in terms of DR.