Nintendo dislikes novel type games in general, they've expressed this, and since the guy that made iM@S DS was sacked (because the game was poor and sold poorly), I doubt we'll ever see another iM@S game on their devices.
3DS simply doesn't have the power to produce something much better than iM@S SP, while the Vita has the potential to produce something like a lighter version of iDOLM@STER 2. Not that I would bother.