Sales will be split as much as mario kart sales are split between console and handheld.

This will be THE smash bros. for Wii U and THE smash bros. for 3ds for the whole generation. people who want smash on his/her home console will buy the wii u version. people who want smash on the portable will buy the 3ds version. and like mario kart, they will coexist perfectly, with many people buying both.

If both versions release at the same time then people will be forced to choose between them. Nobody's going to spend a hundred dollars buying the same game twice, and yes, most people will view the games as identical. You can't use Mario Kart as an example because those versions are released years apart, not at the same time. 

Mario Kart DS and Mario Kart Wii were released 2.5 years apart from each other while Smash Bros U/3DS will be released at the same time. Also the DS and Wii versions of those games were pretty different from each other while one could argue that Smash U Is just a slightly updated HD version of the 3DS game.

you mean argue with no chances of convincing anybody.

Please explain to me what is soooooo vastly different between the two versions other than updated graphics and a few exclusive stages

do u realize about 99% of the things u say are wrong or based off nothing? I would hope having a track record like that would make u a bit more humble but I guess not.

evade the point with personal attacks as much as you want. you called the wii u version a slight hd upgrade over the 3ds version when that's clearly not the case.

I didnt evade the point, look at the first sentance. What is so different about the two versions other than graphics? Each version may have a couple exclusive stages or characters but is that really enough to say they arent essentially the same game?

Smash Bros sales numbers are a really tough call, but heres what we do know.

1. Brawl is the best selling fighting game of all time.
2. The 6.5 year gap between Melee and Brawl made people extremely hungry for a new version and no doubt contributed to its success. Now we have another 6 year gap and the anticipation among fans and the gaming community IMO is even higher then when Brawl came out.
3. Nintendo is clearly pushing the Wii U version more then the 3DS version. They are doing a 3DS one to ensure big sales, but the Wii U version has been showcased the most (for good reason).
4. Sonic and Snake's additions were huge in terms of hyping the game. Mega Man is clearly a hit among fans, but I think Nintendo would be wise to add atleast one more big 3rd party character (Pac-Man, Ryu/Ken, Rayman, Sora idk something big enough to resonate with both the hardcore and casual fans).

My prediction is that combined between Wii U and 3DS, Super Smash Bros 4 will be the best selling fighting game of all time. I also am predicting that Nintendo will release a console bundle with Smash Bros included next Christmas. They have a chance to win 2014 with Kart/Smash alone but bundles at $250 could really launch the system into 3DS level sales.

Same attach rate as their predecessors on Wii?

first you talk about resolution, now graphics. anyway, what is so different about mario kart on wii and ds/3ds, other than graphics. this is still the only smash bros either console will get and sales of the wii u version won't be affected.