I'm not sure that multitrack RealTracks are outside the realm of possibility. I suspect that the main thing preventing them from being implemented is a low "bang for your buck" for PG Music, compared with other projects.
One issue - the drums aren't just mixed on a per-instrument basis, but they're "mastered" via some final effects. So if you got the stems of the drums, you'd lose the polish of the final mix.
This was circumvented with the DI guitar tracks by offering the AmpliTube CS VST.
Maybe PG will offer a mastering plugin with 2013 that could be used with drum multitracks!