After some discussion on the dev mailing list, we've decided to unify the repositories for yt-3.0 and yt. It will still be located in a branch called yt-3.0 in that repository. At some point in the near future the separate yt-3.0 repository will become read-only.
This simply means that if you are using yt normally, from the repository here:
you will be able to switch to the yt-3.0 branch more easily. And, if you currently have a fork of the repository yt-3.0, you'll need to switch to using a fork of the main yt repository. This is easy, just fork the main yt repo (unless you already have!) and push your yt-3.0 changes there.
Just as it has always been, installing the "stable" and "development" versions from the install script will still only put you on the latest stable and development versions of yt-2.x. Additionally, doing "yt update" will not accidentally switch you from one version to the other.
Britton and the yt development team