You're advocating the use of the well explored EMG (electromyogram) interface. These exist and work but the amount of training to operate one is actually higher

You're advocating the use of the well explored EMG (electromyogram) interface. These exist and work but the amount of training to operate one is actually higher than training a person to move themselves. They're used for subvocal speech and no hypnosis is needed. Galvanic skin response is a subset of EMG. The winner would be a plain old analog interface which you can operate with body movement, not to fine yet not too gross. Keyboard is a similar thing but digital. Mouse is analog but planar. Getting higher dimensional than 3D + time is very hard (gestures) and that is what's required for speech or fully operating a machine. Thus the projections.