Context:
People have been asking for IPv6 Support on GitHub since years (probably a decade by now)
... and someone even got so annoyed that they decided to setup a dedicated website for checking this: https://isgithubipv6.live/
genuine question, any reason not to just actually deprecate it then? Like just stop producing hardware that routes IPV4. Chances are there's enough that'll already do IPV4 it won't be a problem, and im sure if you really needed to, you could figure something out.