A recent patent discovered by NeoGAF user Rosti suggests that Nintendo might be working on a follow-up to Wii Music for the Wii U. The patent documentation certainly suggests something along the lines of the disappointing Wii Music. You can view all the documentation details here.
“An image including at least a part of a virtual world is generated as a first display image, a first sound created in the virtual world is generated, and a second sound forming a part of the first sound is selected in accordance with a user operation. Then, control is performed such that the first display image is displayed on a first display apparatus. Control is performed such that the generated first sound is output from a first loudspeaker in synchronization with the first display image displayed on the first display apparatus. Control is performed such that the selected second sound is output from a second loudspeaker.”