For most games and players wireless is ok ... but it comes with increased latency and lag.
speed dont really matter in online gaming so its fine if you lose speed if you change to wireless, but the increased latency is whats matters.
But if you like to play competitively fighting games (e.g. street fighter, guilty gear, blazblue, marvel) wireless wont cut it ... or if you are hardcore enough to recognize the higher ping (I guess 30-50ms more than wired)
Everyone who have tried wired and wireless in those games knows how the increase in ping from wireless can destroy the gameplay in where milliseconds matters a lot (1-2frames more inputlag is enough to make the game unplayable) ...
But if you dont play that games and since not many of that games will come to the wiiu or at least nearly none of those fighting game players will switch to the wiiu to play those games on it, it really doesnt matter ...
Essay Pro