There should be a way to (automatically) import issues from Github to Phabricator's Maniphest.
The description is important to set expectations :)
If we build a tremendously complicated, expensive, difficult-to-maintain bridge between Phabricator and GitHub, it is possible that we will reduce the activation energy required to move a project from GitHub to Phabricator enough to have a substantial impact on growth. Or maybe not.
Our current plan is to build a minimal version of this and see if it gets any traction.