http://www.gamespot.com/forums/nintendo ... -29392912/
Firstly, that game was originally made for the Wii, not the Wii U, so it's not as advanced as Ukulele could be.
Secondly, click the link above to read a discussion on the differences between the Wii and the 3DS version of DKC: Returns. The 3DS version had its graphics and frame rate watered-downed. Playtonic would need to do all this preparation, and potentially more (adding 3D elements etc.), before they could even consider porting it to the handheld.
Unfortunately I don't think it would be worth the time or money; I doubt they would profit from it.