>* It's not PGP.
The most important reason people use the OpenPGP message format is because it is a well accepted standard. Sure the cryptography is not new and fun but it is secure. If you sign something with OpenPGP then you can be sure that those signatures are verifiable on any platform by anyone. The OpenPGP standard has provisions to ensure that the signatures are from a particular entity. This proposal suggests that Github could be treated as a trusted third party. If that is the case then you don't need signatures at all.
Obligatory "The PGP Problem" rebuttal: