Sadly, I don't think there is any risk for them for "losing developers en-masse to competitors".
Everyone who seriously considers to leave the platform has already left when they were acquired by MS and/or continued to work with ICE, and both of those only caused a miniscule amount of people to leave.
This is in no way meant to offend you: You thought about it, but you didn't, just like most people do. It's easy to say you would do something, but actually going ahead and doing it and going against the mainstream is a whole other thing entirely. If that's the data point you want to offer, than it seems like it was just supporting my point.
(And who am I to judge, I've resigned to using Github as well...)
