That's a good idea. The limitation being that your service can redirect go get to a different repository url, but go will still fetch that repository and check

That's a good idea. The limitation being that your service can redirect go get to a different repository url, but go will still fetch that repository and check out what it thinks is the best branch for that version of go: one with the name of the current go version, or master. So you'd have to play some tricks to keep a full clone-able repo with master locked at some commit for each version of each library, rather than just one repo per library with tags. I guess there are some ways to do that where the clones share the objects so you aren't wasting space, though so not insurmountable.