Moved to the appropriate forum,
I get the feeling with the 7D2 new AF system, the obvious next gen cameras are lining up.
1Dx and 5D4 will both incorporate this new AF system, likely with tweeks that match their price.
5D4 I expect will continue to be the MP leader for Canon, with 1Dx continuing to try to walk down the middle of the road between resolution and speed. If 1Dx remains FF with lower res than the 5D4, this will also offer the Canon the ability to have the 1Dx maintain Canons high ISO noise handling crown that it holds now.
As for what the 5D4 needs to remain competitive with other brands, I do not see any reason to feel it needs any thing closer to the 1Dx, it has that in spades. It simply needs Canon to come up with a break through in the sensor dept.
Some people were wanting/expecting this for the 7D2, but IMHO that was the wrong venue. 7D2 is for action at a distance, and massive DR and noise handling are all secondary there.
The 5D4 should be Canons answer to the D800/810 etc. and therefore the sensor is where the improvement needs to be. At this point the 5D3 has so much going for it in all other aspects, you'd need to install the beer, pizza, and pole dancer buttons to give me any reason to upgrade if the sensor is not taking us to the next level.