The catastrophic part really is that Wii U basically has nothing else for the rest of the year in Japan though. *This* was it, Mario 3D World + Taiko + Wii Sports Club + Wii Fit U + Wii Party U are everything Nintendo was banking on this year.
It's going to be a looooooooooong drought now until Mario Kart 8 next April. DKC: TF is unlikely to fare any better than Mario has (another platformer, doesn't even have the benefit of the holiday rush, etc. etc.).
I will say this: There is no doubt Nintendo wanted a release of both Taiko U and SM3DW on the same day to give WiiU a momentum boost in order to increase the baseline.
There is still Monster Hunter Frontier G and Dragon Quest X version 2 yet to be released, but none are platfom exclusives so i dont expect them to do much.
Mario Kart 8 is now the only title i expect will give the U a decent boost in Japan but it is, as you say, going to be a looooong wait. Japan has voted for 3DS and its not looking to change anytime soon.