I know we saw crazy numbers on Wii but come on guys, it's not happening again. Take a look at the Gamecube. The highest selling game was Smash Bros. and I think that sold like, what, 7 million? Unless the Wii-U picks it up and pulls a rising phoenix, don't expect to see numbers any higher than that.
I dont expect anywhere near Wii numbers for alot of games but one thing to take into account is alot of Nintendo franchises have a steady amount of sales regardless of console install base.
3D Mario for example, the revolutionary titles (64 & Galaxy) sold 10-12 million and the direct sequels/spin-off esque titles (Sunshine & Galaxy 2) sold roughly 7 million each. That is on consoles with install bases of 21, 33, and 100 million.
Ever since SNES, mainline Donkey Kong Kong games have sold over 5 million (DKC, DKC2, DK64, DKC Returns) with the exception of DKC3. Thats on console with install bases of 33, 49 and 100 million. Even Konga/Jungle Beat were able to sell over 1 million and those werent mainline games and used an unpopular add-on Bongos.
The first mainline Zelda entry on each console has sold 4-8 million (Zelda 1-NES, LTTP-SNES, OoT-N64, WW-GC, TP-Wii) while the second title on each console sells about half of the first. Thats on consoles ranging from 21-100 million install bases.
Smash Bros is a series that has never sold less than 5 million, again on consoles ranging from 21-100 million. Its going to be on both Wii U and 3DS this time so that may hurt its sales.
Ever since N64, Mario Kart has sold roughly 1/3 of the install base of the console it released on. MK64-10m on 33m install base, MKDD-7m on 21m, MKWii-33m on 100m.
Even if Wii U were to sell 10-15m in its entire lifetime then these series I listed above should all sell 3-5 million, thats worst case scenario. Im pwrsonally expecting Wii U to sell 40 million minimun, if thats the case then all these series should sell 5-10 million and maybe more with heavy bundling.