Not sure why Canon would offer up 2 different 5D cameras just for 4K. If someone is that serious about good 4K, they move up to the 1DX2. That also fits Canon's M.O. of up selling.
It will be one busy FF lineup for sure. 6D2, 5D4, 5D4 4k, 5DS, 5DSR, 1DX2
6 Full frame cameras...
Stands to reason that the 5DS will go away next generation like the D800. While I personally like the AA filter, the internet hordes of pixel peepers hate it. These are the folks that will pixel peep all day and admire the detail and resolution, but ignores the destruction of IQ due to moire. A bizarre contradiction. Anyway, not trying to sidetrack the discussion.
A 6D2 is logical, Canon needs an "entry" FF. Otherwise, that segment is wide open for NIkon's taking.
In Crop...
There's the flagship 7D2, then the enthusiast 80D.
That's 2 in the $1K+ segment.
After that, there's 2 Rebels.
4 crops, 3 of which are consumer oriented.
Maybe this is a sign of things to come - the DSLR market moving toward more specialist bodies with more offerings in FF. With less choice on the low end crops where people buy in huge volume and don't really care.
My guess is, the 5D4 will be one camera, it will have 4K because it has to - but that 4K will in some way or form not be as good as the 1DX2. Or it might be as good, but lacking other video features. Hard to say. This satisfies the video fanatics out there (kinda). 6D2 will happen. Then the 5DS will go away by next generation. They'll probably release the 5DS Mark II, which will be without an AA filter, and drop the 'R' ...but that is a longggg way out. That is a specialty camera, and in the realm that it is designed for - it's IQ will serve the needs for at least 4-5 years.
Four FF body lineup is more realistic I think. Across those 4, what is there that you can't do? Absolutely nothing.