I don't see why cel shaded characters would be particularly expensive to do on an open world Wii U game, there is Breath of the Wild already running on it,and 360/PS3 could have handled cel shading as well.
If the game was made with that artstyle in mind, not getting XC2 as it is on Wii U
They already modded BotW to remove cell shading and noticed marked improvement of performance.
XC2 is definitely a more taxing game than XCX and can be seen struggling on Switch.
XCX also suffers from massive streaming issue if you don't have shit installed on hardware (with very long load times).
there's barely any collision with moving objects as well.
Shadows are not dynamic (like in XC2 really).
We already know that handheld Switch is already more powerful even for games originally made for WiiU, a game like XC2 is going to struggle even more on WiiU without a question.
If you want XC2 on WiiU, there's shit that are going to be dropped or the game is going to run like dogshit with Gameboy IQ (just remember that the IQ on handheld Switch is already VERY low, that's not going higher on WiiU).