Ubisoft has corroborated this dev's story: Rayman Legends really is complete on Wii U and is only being held back so the publisher can simultaneously release across all platforms.
"There are no issues with the game development," said Ubisoft public relations specialist Sarah Irvin in a statement to Digital Spy. "The only reason for the delay is to release on multiple platforms."
Ubisoft has released multiplatform titles at different times in the past, though. When questioned about this, Irvin noted, "We usually release all of our platforms simultaneously (aside from PC). We've made special exception sometimes in the past but it's definitely just on a case by case basis and not our standard practice.
"In this case, Ubisoft recently decided they wanted to release the game on multiple platforms so the decision was made to launch them all at the same time rather than separately.
"I know it's not an elaborate, 'convincing' answer, but it's the simple truth."
So there you have it. Rayman Legends is complete on Wii U, ready to be played, and just sitting there. Look, Ubisoft, it's one thing to bring a platform exclusive to multiple consoles. Only the most dedicated, spiteful console zealots will have an issue with a good game reaching a larger audience. It's another thing to actively punish early adopters that purchased a console to play your game by delaying it half a year when it's actually ready to be shipped.