I would most like the 5D4 to...
Stay away for a little while longer, please!
The UK price of a new 5D3 is already getting scarily close to the Grey Market price I paid a couple of years ago. Don't make me eventually sell it at a loss!!
We're you going to try and sell it as a non-grey market body?
As for features I wouldn't mind in the 5D4...
1.A Sony Sensor (if Canon haven't managed to come up with something that performs even better.)
2.To be able to spot meter on my chosen focus point outside of the center one. (Like the 1DX)
I'm still VERY happy with my 5D3 though.