About NSMB, I believe Nintendo (Tezuka-san?) said around the time of Mario Maker's release that the next 2D Mario would be different, i.e. not NSMB. So, whatever form 2D Mario takes next, I don't expect it to be NSMB in style. For their dedicated gaming hardware, I mean. Still, a 2D Mario is possible at launch as you said. I do think though that given the somewhat lukewarm response to it last time they might wait a bit longer for it rather than position it at launch.
As to 3D Mario, and this is more in reply to the new rumor, but interestingly Miyamoto-san indicated at E3 that we'd probably see the next Mario (not clarified as 2D or 3D I don't think, but it seems he was potentially referring to 3D (though it could be a game combining both styles)), at next E3 at the earliest. Though, they could certainly move up the reveal for it, and I do imagine we'll play it next year. Perhaps they were able to get it ready for launch after all.