A little while back, the PHP development group posted a survey of developers asking them which version control system they'd like to see the PHP project use. By an overwhelming margin, git has won and things are already in motion to move parts of the project away from subversion.
In his mailing list post, David Soria Parra explains:
After 2 weeks of voting and discussion, I closed the votes today. The results are fairly straightforward. Most of the users want to move to a decentralized version control system. [...] I don't want to make a difference of who voted for what. I think the results are overwhelming in favor of Git.
He'll be working on the spec to make the move for the PHP source over to git and is planning a cut over some time in December. Stay tuned to the php.internals mailing list for more details about the move as they come up.