I think the notion that a Zelda with a stylized art style is less marketable is bollocks, to be honest. I mean, look at this:

Is anybody going to try and argue that GTA isn't marketable? Come on. Borderlands? No.
Moreover, if you're trying to attract buyers to the Wii U, washing Zelda in the same homogenized, realistic green-and-brown art style that's flooded the industry isn't the way to do it. Zelda needs to appeal to Zelda fans before it appeals to anyone else. Attracting new Nintendo buyers should be done with new IP and more 3rd party support. Nintendo's absolute strong point is its 1st party IP. Whatever their other faults are, when it comes to their own IP, they know what they're doing. Armchair internet marketing experts don't know better.
For the record, Ocarina of Time is the best selling Zelda because it was massively hyped and the first 3D entry. It was an absurdly influential game that changed the industry forever. It's still being emulated today in some way by pretty much every action game out there. To downplay that and chalk up its popularity to "it had more realistic graphics" is a great disservice. Ocarina of Time came out about the same time as Castlevania 64 and both were 3D action-adventure games. Which one do people remember and why? Castlevania for its dark maturity and realistic graphics? Or Ocarina of Time for its superior gameplay and whimsical storytelling? Twilight Princess is the second best selling Zelda because it was a launch title on the Wii, one of the best and fastest selling consoles of all time, and the first console Zelda game in four years.
Let's also not forget that the first original Zelda game on a system has always outsold the second, no exceptions. That applies to both consoles and handhelds. Ignoring all of that and assuming that OoT and TP were the most popular because of realistic graphics ignores Majora's Mask, which was even darker and more mature than OoT, but sold poorly by comparison. There are other market reasons for that. It has nothing at all to do with art direction.
Finally, the E3 2014 reveal of Zelda U literally dropped my jaw. It is easily the most breathtakingly gorgeous Zelda game ever made, and one of the most gorgeous games ever made, period. I'll take it over Twilight Princess HD any day.