Even I don’t understand the 2nd question, as its neither go gettable (as that probably will fail due to missing deps or wrong versiom of deps), neither it builds without modifying GOPATH (its just that in this case the build wrapper solves the problem).
Currently it’s certainly go-gettable. go get github.com/syncthing/syncthing/cmd/... works for me at least. Making it build regardless of source location would most likely prevent that though.