Super Smash Bros. for Wii U could arrive in the same Spring 2014 time frame. Speaking to Neckar-Chronik (via NeoGAF), Bernd Fakesch said, "At Christmas we now want to inspire with titles like Wii Party U, Wii Sports Club, Wii Fit U and all of course Super Mario 3D World, the classic Nintendo Family for the new console. For next spring two more big license games are also announced for our TV console with Mario Kart 8 and Super Smash Bros."
No word yet on when Super Smash Bros. for 3DS will arrive, and which territories Fakesch's mention applies to. We've contacted Nintendo for more information.
Nintendo recently revealed the Skull Kid Trophy Assist and a Super Mario Galaxy stage for Super Smash Bros.
So apparently, both are Spring 2014 releases; I think Nintendo might release Mario Kart in March, Super Smash in late April.
This would greatly help the Wii U's commercial prospects.
I wonder when SSB 3DS will release?