Thanks for bringing up this topic!
I am personally not really good in writing and structuring great documentation, but I will of course help if I can — at least with answering questions, checking for correctness, …
Regarding tooling: my learning from many years of open source (and various documentation efforts) is, that it is rarely a tooling question. Thus I would propose to stay in our current toolset (restructured Text and readthedocs), and rather focus on content.
I agree with your „centralization“ thinking — so let‘s just focus on putting all the relevant docs in the Neos package… I‘d say this is pragmatic and could work well for now
Just my two cents,
Curious to hear further thoughts,