Could we be seeing Nintendo's answer to LittleBigPlanet?
http://www.nintendoworldreport.com/rumor/37616/mario-maker-to-be-revealed-at-e3
A photo has supposedly leaked out from Nintendo's E3 booth, and has revealed a possible new game entitled Mario Maker.
Judging from the photo provided, the game involves having full control of the assets from the original Super Mario Bros., and being able to make your own levels by placing pits, enemies, blocks, and more wherever you like. It is unclear if they intend to include other Mario titles.
Other character art seen in the picture, such as Kirby, Animal Crossing Villager and Pikachu, are reminiscent of Smash Bros. character art, a game that all three characters are confirmed to be in. Nintendo has yet to issue an official statement.