Assuming you are right and it's just an added feature that has no effect on the physical design of the controller then sure more options are good yadda yadda..Unless the controller pieces don't have all the buttons a Wii U GamePad does, I don't see how this could possibly be negative news. You'll still be able to use them like a standard controller, and games that aren't Just Dance will probably support standard control schemes.
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But how often do you really use the 'motion controls' that are tacked on to standard controllers like the Dual Shock 4 etc..if the answer is never or almost never then it adds some cost to the design for no reason which is even if relatively small, impacts the build costs of the whole system which is clearly a priority or it would be competing with MS/Sony.