Sonic & Mario comes out today right?
Which is why they hopefully have more games lined up early this year including the big hitters smash and mk8. Dk is coming in February so if we get one of those other games in April at least and another by June hopefully the momentum stays higher then it was last year where it really bottomed out due to the launch window games being pushed to august+
That's in the US. At the moment, DK has no month for Japan. My guess is March since the Western releases from Retro and Monster tend to be ~1 month late, however, they may bring it to launch close to PS4 on the 22nd to try and steal some thunder, since PS4's line-up is pretty meh (at the moment, for launch, in Japan). Wii Fit U is like February 1st at retail.
Mario Kart is listed for Spring, and I imagine they'd love to have it out in March to give a final push to their FY numbers BUT they may prefer it in April or later (presuming it's ready for March, but delayed) to try and give the new year a positive spin and push off some momentum for the new year.
Of course, given Nintendo's predilection to have 1 retail game per month, I imagine the start of next year will go:
Jan: Nothing
Feb: Wii Fit U
March: Donkey Kong
April: Mario Kart
But that, to me, is almost a worst case scenario.