The picture actually seems rather plausible to me for several reasons:
A) Despite the low quality of the photo, the Smash Bros. logos and renders appear in the correct places in a professional manner, with nobody (yet) able to show that the background originates from another E3 photo.
B) Nintendo already has a downloadable pixel art/rom hack series that's met with moderate success.
C) As explained in McWhertor's other tweet, it could fit the bill of a game utilizing NFC figures; buy figurines of certain characters (which could be used with other games as previously stated), and you'll unlock new tile and sprite sets for making levels. Plop Link on and get NES Octoroks and a Bow powerup, etc.
D) It's a low key and "mundane" title. A neat idea, for sure, but not one that someone would go to lengths to fake. Normally Nintendo fakes consist of overwrought "epic mature" fan art of Zelda with a stupid subtitle, or a list of games including sequels to all of the fan favorites from the N64 and GC days.
It could still be fake (Thursday is kind of early to put up logos of unannounced games, the original source for the photo hasn't yet been found), but it's more plausible than any tilted paper fakes so far.