I'm also pretty sure that if we see a Smash release this year, it'll be a re-master/re-release of the Wii U/3DS versions. I never owned a Wii U, but have played the 3DS version a little. I only own an original 3DS, and the scrren size made playing it too much not a particularly attractive proposition so I'd welcome the chance to play again on a bigger screen and with all available features and characters there for the unlocking.
I'm wondering if it's a good release to showcase their paid online offering, given that Smash has historically had a large multiplayer base. If the two were released around the same time, I think it could draw a lot of people into their online ecosystem and hopefully lock them in for the full yearly membership.