Shaking up the community right now would probably make efforts to continue Vim’s development more challenging, and make it more likely remaining contributors switch over to Neovim.

Google groups I can't comment but Github is a relative new thing. They were also still accepting patches on the mailing list(I believe the github pull request were mirrored to the ml or something like that). Bram was often replying to issues and pull request via email so github adoption doesn't seem to what Bram wanted. So no migration away from github.