Yeah... I summarized the best I could here:
https://github.com/astropy/astropy/pull/16013#issuecomment-1936723921
tl;dr --
Impact on our users: Probably none. As we only actively support v6.x series now, there is very little reason for users to need docs for older versions. If they have to, the redirects should satisfy most of them.
Impact on downstream maintainers: Probably very little. I don't think anyone hardcodes astropy doc to a specific version URL. We have always encouraged maintainers to use intersphinx which should either give them "latest" or "stable" versions.
Impact on astropy historians: Major impact here, especially for documentation purists. But I know zero astropy historians, so while impact on them is high, impact on us is probably very low.
In the end, this is totally my bad and I take full responsibility. I deeply apologize.