I think this boils down to “what do you do if you realize the documentation for v1.1 says that some feature does X when it actually does Y, but you’re already on version 2.2?”
If v1.1 docs are tied to the version tag in VCS, that incorrect statement cannot be fixed.
And it seems that fixing that forces you into backporting documentation even if you don’t release and maintain parallel versions of your software, which… kinda sucks.
To be honest, I much prefer docs in the repo, because it facilitates code review — a good patch touches some implementation, some tests, and some docs.
The downside when only the latest few versions of the software are supported and only the very latest docs are maintained is that historical docs will probably not be fixed.
