sourcehut is already a viable alternative to GitHub, with a valid business model and it's entirely open source.
It focuses on power users and tries to simplify workflows for develoepers as much as possible.
It's not unthinkable that more and more projects start using either sr.ht or a self-hosted instance as upstream.
This patch intends to add support for USES_SOURCEHUT and, from my limited testing, it works quite well for custom ports.