I think the Wii U will be more in line with Nintendo's normal sales numbers before the Wii. The Wii was a one time thing. I don't see them replicating that success.
So it'll be more along the lines of N64 or Gamecube and I think Nintendo will be fine with those numbers, perhaps a little more than those would be good. They won't be swimming in money like after the Wii, but they'll make profit and move along no problem.