Other than someone with serious finger/hand issues, I'm having a hard time imagining a disability that would prohibit someone from using a mouse/keyboard as input but would leave them able to use full-body gestures.
It is not necessarily a bad idea, and it would not have to be restrained to people with disabilities. The way Google presented the idea was fun but it did make some good sense: it would make us, couch potatoes "have to" move.
