On the GitHub Support forums Kastner has proposed an idea - making something similar to gethub gems but for PHP:

Just like ruby/gems, PHP has a packaging/distribution system called PEAR. I think that running a pear channel would help the PHP community with things like GPL extensions, as well as increasing participation in the community. Thoughts?

There's already thirteen comments on the post, all supportive of the idea including interest from the GitHub folks themselves.