I've used something very similar in Go. I can't point to it because it's an internal repository, but it allowed for relatively smooth co-existence between a v1

I've used something very similar in Go. I can't point to it because it's an internal repository, but it allowed for relatively smooth co-existence between a v1 and a v2 of a particular package that had one aspect that was hard-to-upgrade, but also, generally rarely used compared to the rest. The rest of the types were fully identical because v1 simply re-exported the v2 types, so Go only complains if you try to cross the streams with the specifically-changed but rarely-used types, which is exactly the complaint I want. In the case of Go I'm not sure if it's important that v1 specifically re-export the v2; I think it would work equally well either way. But it's at least very similar.