I'm looking at the specs of the just-announced 80D (45 AF points (all cross type), 27 of which will work at f/8, and (I assume just the centre point) down to -3EV). In terms of cross type points, number of f/8 points, and low light AF that's (on paper) better than the 5D3 and original 1Dx.
That surely bodes well for a 5D4; I thought they might use the 1Dx II AF system but, say, leave just the centre point at f/8, but it doesn't even look like they could do that now (otherwise it'd look worse than the 80D in that area). I guess competition is good for consumers. Who'd have thought it eh?