Fascinating, I wasn't aware EEG was so susceptible to signals from outside the brain. I knew it didn't have the highest SNR, but I guess it does make a lot of sense that a big reason for that would be it contamination from electrical impulses from the rest of the body.
I would even say EMG is more useful as a HCI channel, except in the most extreme situations like lock-in syndrome or late-stage muscular dystrophy.
EMG is way more easy to control consciously and as Humans we probably have hundreds of degrees of freedom in our body for some kind of EMG, not all of it conveniently accessible of course. Controlling what consumer grade EEG devices can pick up is a lot harder. Brainwaves are "feedbackable", but that usually means changes in mental state like awareness, concentration, relaxation and so on.
Muscle movements, think talking, chewing, or blinking, generate voltages orders of magnitude higher on the scalp than sources from neural activity inside the skull.
