Hi Joe,
Sorry for this very late answer. You're right that gitplugins could be broader than Moodle, and could be very slightly adapted to fit in most of php applications.
The fact is that many "big" php applications with a lot of plugins available already have such a mechanism, often using Composer. As Moodle HQ as not made this choice, despite of some discussions, I think gitplugins can be useful for Moodle.
Besides, I have plans to connect gitplugins with Moodle specific plugins inventory features later, but have not coded that for the moment.