Well, you can buy the camera alone with the gimbal for the P2V+ so there's NO reason why the P3 camera won't be available separately, the questions is will the wiring harness be compatible with the P2V+.
At some point they will offer replacement parts, just like all the other Phantom versions. I expect it will be a while because the first priority is simply building enough of the silly things to keep up with the demand!
There are kits now that will allow you to use a GoPro camera with the P2V+. If there is demand, it's just a matter of time before somebody makes an adapter to allow you to use a GoPro with the P3.