The thing I find to be the biggest concern is the fact that if your mobile goes kapoof or gets stolen or whatever, you are, as you say, locked out from the game. And as has been the case in many MMOs as of late, getting any kind of support can take hours, even days from personal experience. But then, I am not sure there is a way to prevent that from occurring, sadly.

As for the extra bit of loot from apps, I don't see a huge problem with the Rift Mobile app. You can get a tiny bit of planarite and some other bits and pieces here and there. For the most part, I am sure there are people who end up with some epic crafting bits here and there, but I am fairly sure that the chance of getting such booty is a very, very rare occurrence. It would be nice to see access granted to users without the proper smartphone via a web-interface or something.