I don't see huge gains coming. Engines which maxed out the 7th gen will already be close to maxing the Wii U. It has double the RAM and so far from what I can see the ability to generate prettier lighting...and that's it. Sure, put in some real budget into a game and picture GOW 3 but with better textures and lighting. Hey that right there looks nice. But by the time such a game appears the Naughty Dog proper shows what they have up their sleeve.
Console gamers are willing to sacrifice visual quality anyway, It just seems to be by degrees with some. WiiU games won't be any uglier than PS4 games. They'll just being using muted in comparison tech to achieve their beauty.
I mean we're in an era where even handhelds are achieving stuff like Revelations and Uncharted.
Ugly and beauty are only degrees today. Bigger emphasis on cohesion of assets will be more important going forward.