I feel like this "cannibalization" argument that always comes up, fails to take into account, that it' not about cannibalizing iPad vs. MacOS. I think it would be more about unifying the MacOS and iOS userbase, making it an even bigger total market for app (and games) developers to target. Also, don't forget, that expansion could also come in the shape of PC users choosing Mac instead, if a real (and good) alternative existed to touch-based PC's, such as the Surface Pro that I'm typing this os.