This post (and especially the tweet announcing it) imply that there is simply no way to make Badger v2.0.0 work with both modules and dep. This turns out not to be the case. If you wanted to make Badger v2.0.0 work fine with both Go modules and prior tools, the solution is to put the v2 code into a v2 subdirectory in the root of the repo. Then both Go modules and non-module-aware code fetches will find it. See my comment from June 26 for details.
That is, there is a way to avoid breaking any users. The approach you’ve chosen instead is fine as long as you realize that you are choosing to break dep users and likely users of other pre-modules vendor-maintenance programs. Perhaps you are choosing it for what you think is a good reason, like not liking to have a v2/ subdirectory. That’s fine. Just understand that you are making the choice. You are not forced into it.