Can Versions.toml point to git branch instead of fixed git commit?

true, however I for developing in a shared environment (cross OS, cross Machine, cross user)
a registry is useful for sharing

in the registry I need to specify versions for things to work at all, even if I don’t have any stable version yet.

It would be super natural to instead point the registry directly to a develop branch (or master) so that people can try out my develop version by just taking my registry and everything works as normal.