Detachable controllers could have some kind of new gimmick to them, some kind of new layout maybe.
A mobile console with a large screen on it that goes anywhere with detachable controllers that invites people to gather around and play together is a very Nintendo-like concept.
Ubi Soft already announced Just Dance for it, so the controller probably has some motion component to it, unless they're using 10+ year old Wiimotes which I doubt (time to let those die).