There's no doubt Elon is a dreamer; but a lot of his dreams have panned out pretty good and I think there is more to come. Others have also worked on various forms of man-machine interface, but usually to replace some deficiency (like enabling the deaf to hear, blind to see, etc.)
Anyone remember hearing Stephen Hawking speak? That was a man-machine interface (granted a very crude one). He had "Lou Gehrig's" disease, which is "rare", but there are some 15,000 Americans living with it today. Hundreds of thousands have regained their hearing with cochlear implants, another crude man-machine interface.