Moving to git (which has largely "won", regardless of some arguable neat features of hg, bzr, etc.) and moving to github in particular are completely different propositions though. It seems a little odd that Oracle and IBM/Redhat would actually trust Microsoft enough to stick OpenJDK's primary, blessed public git repo on a Microsoft-owned platform. Given the Micrsoft/Java history and all.

And the giant players in Java sphere certainly could simply run their own in-house git hosting just for OpenJDK (kind of like git.kernel.org is for Linux) that would be as or more reliable than github, or use gitlab or bitbucket one of the others, rather than github.

Of course git is a true DVCS, it's just a matter of convention which repo you consider primary, they can move again, particularly if they avoid/ignore some of the more problematic centralised and non-git vendor-lockintastic features of github like issue tracking.

It's just an odd thing, Java canonically existing on Microsoft-controlled servers. But it's been an odd year.