My guesstimate is 250K. However I get the feeling from the Nintendo forums on the web that wii u owners are so bloody desperate for any new half decent game that they are willing to get this over Pikmin.
If marketed well so the few wii u owners that haven't heard about it get wind of it I would probably say 0.4m is a possibility.
Although it is not terminal if this game flops, if marginally successful it can really be a small but much needed boost to the wii u.