Rumor has it 10 or so developers have returned their Wii U dev kits. As posted a few days ago Avalanche Studios (Just Cause series, and one of the devs returning the hardware.) said their dev kits were gathering dust. This was apparently due to no idea on how to use the hardware, no ideas, and little to no contact from Nintendo. Avalanche Studios believes the Wii U is a "cool" idea but not a step in the right direction for their company. However this seems to be the main issue with a lot of 3rd party devs, and could be the reason for the. Excuse me.
The other devs that returned their kits (If there are any.) have yet to come forth.
Source
Hazing no gamez
The other devs that returned their kits (If there are any.) have yet to come forth.
Source