Sounds like the hardest part would be making sure it isn't a fire hazard. That being said I don't like my feet being warm while I sleep, so this project misses for me by being a sock. So close.
I'm sure the same benefit could be gained through a leg band. For me, I tend to move around in my sleep, so I wonder if it would work.
Pretty much no one moves around during deep enough sleep, it is just when your sleep cycle lightens up that you move around in your sleep. The same tech still works, it just might not be able to detect all the stages of your sleep as effectively.