I think you’re overestimating how much people pay attention to the body part of the import paths. Since there have been a quite few projects that implemented a sort of redirect (i.e. ‘vanity’ imports [0]) most people’s eyes just glaze over the small change in the URL.

I would strongly suggest using /v2 at the end. /v1 not existing on *.golang.org is not a problem in practice, but if it ends up one you could just set that up as a vanity import pointing to github.com for the old version.

[0] https://sagikazarmark.hu/blog/vanity-import-paths-in-go/