The big pre-E3 Nintendo rumor is that they'll be announcing something called "Mario Maker," which may or may not be an SMB level-editor app for either WiiU, 3DS or both.
Sounds fun! Also sounds like something that would've been a best-selling straight-up CLASSIC on the SNES/N64 or a solid fan-hit on Wii/DS but will now likely be a minor "huh, nifty!" a'la NES Remix. Still sounds fun though... and it ALSO sounds like something I predicted on this show five years ago. Nifty!