Well, I believe the rake is still a better deal at most stakes at PokerStars, so that should play a factor. Also, no one really knows what to expect with the new Black Card yet, so at the moment the best deals are still if you can hit SN or above at Stars.
Basically, I think what they are trying to achieve is reward systems to benefit different targeted player pools. For the people that were settling into the Gold/Platinum levels at Stars, it's probably a better deal to play at Tilt at the moment. Considering rake structures and higher level rewards, those that are at bronze/silver or SN+ are probably better off at Stars.
But honestly, this is mostly just conjecture on my part as I haven't done any real calculations. There will probably be some more detailed analyses coming out in the coming weeks/months.