I could care less about a 5D IV, and I have my doubts there will be one. The 6D will probably get an upgrade.
I suppose there are marketing guru's at Canon that are deciding if they need a body between a new 6D II and the 5Ds.

Personally I am hoping the next generation 1D body is released soon. Earlier this month I went elk hunting, I took the 5Ds R with me. I regretted not bringing the 1D IV because of the brutal conditions. Single digit temperatures, near blizzard conditions and it was always wet.

In the new 1D I would like to see;

Dynamic Range, we can make fun of the Nikonian and Sonyites that pound that drum. Camera's do not capture even close to the range you can see with the human eye. This is something I would like to see improved in any future bodies.

Higher ISO performance would be good, but no doubt we are trading that for mp. I want both.