This newly uploaded YouTube video of the Mavic Pro gives a perfect look at how the Mavic Pro performs indoors. I'm going to go ahead and say that it definitely performs better than the Phantom series of drones, including the Phantom 4, in regards to stable flight indoors. Completely locked into it's position, even while turning on the spot at an very low altitude. No drifting at all.
I know, it looks crazy stable in that video. I also can't contain my excitement for the Mavic Pro. It would be very nice if we could have our drones in our hands before the New Year but at this point, it's all down to DJI and their shipping speed. I wish the Mavic Pro didn't release so close to Xmas, there'd probably be way less orders and DJI would have no problem coping with it all.