There has been alot of talk about Mario Kart/Smash Bros being the games that drastically improve Wii U sales but im not so sure they will. Currently Wii U is tracking behind Gamecube and I believe that these two games will push Wii U sales to GC/N64 levels so about 20-30m.

I know alot of people will say "but Mario Kart Wii sold 34m!!!!!". The thing with that game tho is that it fell in line with the mass market/casual games like Wii Sports, Wii Play, NSMB Wii, Just Dance, etc and benefited greatly from that market that seems to have left consoles for Smartphones/Tablets.

As for Smash Bros, it sold 12m on Wii but this time it will also be on 3DS so that will likely take away some of the console versions thunder.

All in all I believe these games will sell what they did in the pre Wii era. Mario Kart on SNES/N64/GC sold in the 7-10m range and Smash Bros on N64/GC sold in the 5-7m range.

I'm not so sure about Smash Bros. - including the 3DS version it will likely manage over 10 million, but the question is how much the Wii U version will sell compared to its handheld counterpart.

MK8 I can see doing around 9 million. 8m bare minimum.

Around what the games sold on GameCube.

It depends if there is a bundle with smash bros or MK 8
that would sell

Mario Kart 8 - 8m

Super Smash Bros U - 7m (3DS version will hurt it)

My guess is that Nintendo ends up making bundles for both so the numbers for Kart will be closer to 15 m. and Smash Bros will be about 10 m. These NSMBU bundles sold extremely well, and that was a game that was already out for a year, not to mention that bundles are a big reason why the 3DS has done as well as it has.

i think they will sell well above its GC counterparts. 10m for MK8 and 8m for Smash

No matter what it sells it will be a flop.

better than GC nowhere near that of Wii era of course. Not sure about Smash, i think the 3DS version will really eat into the sales of the Wii U version. I think people will hold out if they have a 3DS already and will just wait to get the Wii U version

I think Mario Kart will get about a 50% attach rate by the end of 2014, a good question is will it drive Wii U sales? I'll play it safe and say 4.5 million copies by the end of 2014.

Smash will get maybe 25-30% attach rate since it's a fighting game & not as accessible as MK, again, will it be a system seller? I'll say around 2.3 million by year end.