You may be interested in the PR here: Example of supporting dep and modules by cep21 · Pull Request #128 · mediocregopher/radix · GitHub and the conversation here: Broken govendor/dep.. vendor support · Issue #53 · mediocregopher/radix · GitHub
It is an example of modules which do contain imports of the module itself, a v3 repository, and supporting “go get”, “dep”, “glide”, and go modules while using go modules correctly with a /v3 import path.
It involves using “goforward” on the old location, but otherwise works fine.