Personally, I have zero use for this type of app, in either a paid or free format.
I have iPod, WunderRadio, Pandora, Last.fm, AOL Radio, and the Sirius/XM app already on my iPhone. I get enough music/talk radio. And when I come across new artists, I buy the album so that I can control the sound quality (at least to a degree).
While I haven't decided to delete any of the above apps, I don't use all of them daily (the iPod/AOL Radio/SiriusXM apps I do).
That being said, I doubt Apple will let it through the App Store, unless as others have said, the subscription goes through the App Store as well.
And.....then AT&T might have something to do with the program's approval, either from the standpoint of wanting the subscription to go through them.....there's also the added overhead of traffic on their network. They may have something to say from Spotify being allowed, just as the issue with tethering.