I wonder if there's a set of API hooks they could expose to allow third party applications to handle more advanced code review techniques? I would totally understand GitHub not wanting to implement a full Phabricator/Gerrit review feature set, but maybe they could make it easier to integrate other services for it.
GitHub has become the de-facto place to host open source projects. Improving the tooling around code merging, seems like a no-brainer, and a huge potential win for the projects using it, especially the larger ones.