Exactly, this is why you need a different sokution for a different group of photographers. It is impossible to produce one camera that will be perfect for professional sport, landscape and street photographers.
Yes you can. It would just require extreme bandwidth (for 54MP at 14fps or so), a pixel binning option (for lower resolution shots which still take advantage of all the pixels to minimise noise), a slimline, form-fitting removal grip and a lot of features that would make for a very expensive camera.
Personally, I'd prefer a multi-camera approach. After all, the 5D2 and 5D3 aren't even really from the same class of camera - one was a high-resolution (for the time) IQ monster, the other a general-purpose body emphasising AF and other features over IQ.
1Dx2: 32MP, 14fps (if moving mirror) or 25fps (in 8k video mode), top-of-the-line AF, dedicated action camera
3D: 54MP, 5fps, top-of-the-line AF, high-resolution stills camera also capable of capturing action (like the D810)
5D4: 32MP, 8fps (possible 8k video too), top-of-the-line AF, general-purpose camera (like the D700 or D750)
6Ds 54MP, 4fps, basic AF (like the 5D2)
6D: 32MP, 5fps, basic AF, budget model (like the D610)
As well as a mirrorless version of the high-resolution version, which would be similar to an A7r with attached Metabones, but with much better/faster AF from being Canon native.
In other words, one action (1D), one high-resolution (3D) and one general-purpose (5D) camera at the top end, as well as the same sensors put into a basic body for those who don't need the features.
Too many cameras? Well, Nikon does it...