Nintendo has announced today that NFC figures, much like those usable for Skylanders and Disney Infinity, will be detailed at E3. The figures will work on Wii U and 3DS, and can transfer data, such as save games and other goodies, to and from games.
The Wii U gamepad has built in NFC, and the 3DS will have a separate purchasable reader. Details are scarce otherwise, but I’m betting that this is what Sakurai was talking about when he said you could transfer things to and from both versions of Smash 4. More info after Nintendo’s E3 Direct!