I'm curious to learn what sort of issues you've seen when trying to use modules instead of GOPATH? Most of the migrations I've done have been pretty seamless and the few that had issues where all easy to resolve with a few replace directives or similar.
Anyone who has written any tooling that works with Go code saw issues because almost everything changed in this regard. I was maintaining vim-go at the time, and quite a few changes were needed there too. I don't have a list of issues at hand because it's been a while, but generally speaking the only reason things went "pretty seamless" is because people spent time updating the tooling.
