It will take a bit of time to get a PHP driver going. Hang on!
While I don't know what they have planned. Might I say part of the issue might be PHP's _extremely_ poor protobuf support.
There are a few ways to deal with this issue -- contribute to the PHP protobuf library, or have an alternative layer on the server that accepts a more portable but less efficient serialization format. It's a little frustrating, but wouldn't be too difficult to solve.