If I recall, the main selling point of the 7D when it was released was it's superior redesigned AF system and FPS over the XXD. Here was a solution to those in the prosumer segment that couldn't afford a 1D series to afford a better AF system and were complaining about the old 9 point AF system. It was definitely a more action/sports/wildlife kinda camera. Right now, I would say Canon's AF offerings are on-par - so really is a 7d mark II even needed?
5D3 AF would be a huge increase. Likewise 3-4 extra FPS would be game changing for those who need the speed.
I'd also be happy if Canon pulled a move like Sony did with the A7s and dropped the sensor resolution, but gave amazing low light ability. The ability to take a useful shot at 6400+ ISO would greatly enable action shooters. The 500L is a bright, constant f/4, but that still isn't always fast enough and high ISO performance would greatly enhance it's usability to freeze motion.
With my 6D, I notice every day how much slower it is in FPS and AF than my 7D. The low light performance is stellar though.