A workable fork would most likely require standing up new servers that would be isolated from the existing Signal user base. I think we'll see a handful of forks very shortly and it will be interesting to see how the new maintainers navigate the current landscape.

There is already a fork, it's called Session, but it's decentralized, so there's no requirement for servers to be stood up other than introducer nodes AFAIK. https://getsession.org/

This outright hostility towards third-party clients was how I knew that Signal was just a wolf wearing open-source clothing. Glad I stayed far far away.