Just wanted to say that this doesn't impact OpenTF too much. It's an extra step we need to take before a stable release, but long-term it'll make us more decoupled, which is great.
As someone else commented, all providers and modules other than Hashicorp's are hosted on GitHub and the registry is just a "redirector". We'll do something similar, other than some special handling for Hashicorp's providers.
Also, I know you want us to finally publish the repo - we're working very hard to make this happen and it should be a matter of days now.
Disclaimer: Work at Spacelift, and currently temporary Technical Lead of the OpenTF Project, until it's committee-steered.