A - I don't think revised rulebooks are particularly likely. The stuff they want to change is too messy and would require too fundamental of a rethink to the design.
B - I think significant revision re: secondary books like a Xanathars 2 is extremely likely. They'll keep it optional within 5E.
C - Yes, I think 6E was already closer than we though, internally in WotC, at least as an option, and I strongly suspect that, for WotC, the rest of 5E will be that "let's try out more wild ideas" phase that D&D enters at the end of an edition's lifespan. We won't see the impact for 8-16 months I'd guess, but then I suspect we'll see wilder stuff.
This may be wishful thinking on my part, but I don't think so. Every previous edition, without exception, started doing this in the last few years - once you start making big changes and additions, even if they're purely optional, you want to make more, and generally the public likes it.
If they do bother with a revised, there's no way they'll do it for less than a 5.5 or 5.75 (where Pathfinder is regarded as 3.75E). It'd be backwards compatible, but more in the sense that you could still use all your 5E adventures with it than every piece of 5E material. It's the adventures that people care about with backwards compatibility.