I think this is a mistake. Packaging should come from a central server (that can be overriden with a mirror). Allowing downloads from adhoc git repositories is a real pain. First, it makes mirroring the package repository impossible. Second, it makes it difficult for companies to disallow certain packages in a centralized fashion. Third, it makes distro packaging a royal pain. And finally Git simply wasn't built for the this kind of work, compressed tarballs happen to work great for this purpose. Git's mutable history also presents other challenges for pinning to specific versions of packages. Simply put, sometimes a central authority has advantages.
That all said, vendoring alleviates most of these problems for apps and some of them for libraries. Reusing tools does make it a little easier to get started with too. I'd hate to see these features removed in whatever go get becomes in the long term.