The R6 is an extremely good camera, and the only real reason why it "needs" updating is the perceived notion that 20MP isn't good enough, i.e. not as big a number as the sensors is Nikon and Sony competitors. I doubt very much if anyone will notice any difference in real terms between the 20MP sensor of the R6 and the 24MP sensor of the R6 Mkii.
On paper, there don't appear to be any other major changes, apart from the unexpected and unusual addition of a digital teleconverter, this being the first time that such a feature has been included in a pro-level camera. I suspect that it may incorporate some AI software that will improve sharpness and detail rendition over and above what would be normally expected from such a feature.
As for a "R5 Mkii" - the R5 is a superb camera, when it gets updated I'd expect only a few minor enhancements. Sometime in early 2023 we'll probably see the announcement of a hi-res "R5S", and I'd expect the "R5 Mkii" to be announced alongside it.