The thing that I'm hoping for is that this was a panic buy because somebody at Facebook got spooked that a killer rival VR social app might render FB gradually irrelevant. So the purchase was a defensive move only, to make sure that they leading VR hardware comes from their own house and can't be used to undercut them. I think it's quite possible they didn't have any concrete social VR application in mind. This would not be a strange move for a rich and paranoid company. I'll call this the "playing defense" scenario.
If FB really is just playing defense, then maybe they'll invest in Oculus to make sure it's the VR standard, but they won't really profane it with stupid Facebook shit, because they don't really know how to do that anyway, apart from maybe some app that nobody will really use (except maybe webcam girls).
Of course, if they really are playing defense and they realize that VR isn't really a treat to their market, maybe they will cut funding from Oculus and let the project rot on the vine. That's a real danger, and it would set back the field for a while.
On the other hand, maybe Facebook knows exactly what they want to do with Oculus, and they are about to bend the project to their evil will. Whatever that would be, I'm sure I would think it's an abomination. This is why the gaming community reacted to badly to the announcement. But even if this is true, it might not be a total catastrophe. The important question is whether the technical issues that make VR so hard (latency, pixel persistence, motion tracking, etc.) will be getting a lot of attention, or a little. If it is a lot, then even if the final product is larded up with stupid Facebook crap, a hack will exist to remove it, thus producing an excellent VR headset. I just wonder how much FB is willing to invest in fundamental VR research and hardware improvement. Hopefully they won't neglect this side of things.