Sometimes we lose parts of our body from accidents, or worse, intentional mayhem. In the earliest of times, we'd make a crude prosthesis to allow the person to function, at least marginally, again. A peg leg wasn't as good as a real one, but at least one could hobble about without falling over. A hook for a hand allowed you to at least grab a sandwich, and operate a few tools. A patch, or a glass eye, allowed people to not vomit from seeing your empty eye socket. You still couldn't see, but you didn't look like a freak anymore, which helped immensely.
In modern times, prosthesis technology is way better. You can get a leg that resembles a real leg so strongly that most people won't notice the difference. (Well, when you're wearing shoes and pants. Take off the shoes and there's an obvious mechanical joint at the ankle, and if you wear shorts, the knee is also obviously mechanical.) You can get a rubber and metal hand that allows you to handle objects as well as your flesh one originally did. The hand can even "feel" heat, though is otherwise deficient in the sense of touch.
I think a team of prosthesis crafters and neurologists should team of for a next generation of prosthetics that tie into the nervous system. We could have artificial hands that have a true sense of touch, one that works as well as our flesh hands. We could have "eyes" made of camera that allow true vision. (We currently have cameras that are on the sides of dark glasses, that have an inductive tie into the nervous system, allowing a very low resolution greyscale vision. It's enough to walk around and not walk face first into a wall. Most sightless people who've received it describe it as more distracting than useful.) Neurologists would be part of the team because the prosthesis would have to receive its operating signals from the nervous system, and send data back, and using the part would be not any different than using the part you had before.
I'd suggest having the prosthesis surgically grafted to remaining bone and muscle, making it a replacement for what was lost. It should have integrated blood vessels, with "vampire" power support, a system that powers itself by extracting glucose from blood and burning that for energy, as your body does now. This technology exists now, but is rarely used.
And ultimately, I'd like to see a cyberbrain developed. A part that attaches to my nervous system and extends the ability of my brain. I know that this is possible from experiments in which mice brain cells were grafted onto electronic chips, and they integrated into each other. The resulting system was then taught to operate a flight simulator. Immediately, I would expect to achieve sharper senses. Vision uses a huge amount of our neural processing ability, but if one loses it, the brain concentrates on the other four senses, which become significantly sharper. It would also, as a mechanical part, be able to interface with non-brain objects as well. Perhaps it could connect to a computer, which I could now operate by thinking commands.
At some point in this process, I think we could develop prosthetics that are superior to our original parts. Imagine having the arms of a body builder, but not needing to exercise. Camera-based cybernetic eyes will never develop Glaucoma, cataracts, presbyopia, or macular degeneration, and would also lack the "blind spot" that our eyes have from the retina being on the wrong side of the back of our eye. Cybernetic ears could be made that respond to frequencies higher or lower than current human hearing allows, and could be made arbitrarily more or less sensitive according to the needs of the situation. (Or could even be turned off for meditation or sleeping. No more being bothered at 4am by some obnoxious guy with his stereo up way too loud.) Even obesity becomes a thing of the past. If you eat too much, you could plug yourself into the wall and power your house for a bit. (Your power bill promptly becomes replaced with your grocery bill.)
I'd also like to see cybernetic replacements for organs, which could save millions of lives worldwide. If I had an artificial heart as good (or better) as my current biological one, I'd cheerfully replace it, and my original biological one could keep alive a person who would otherwise die. (This assuming that the dying person opposes cybernetic replacements as "unnatural" or something. More likely, those dying of heart disease are the ones who wind up with artificial hearts.) Artificial kidneys would make the expensive and difficult process of dialysis a thing of the past. Artificial livers would make hepatitis a thing of the past, as its mechanical nature proves impossible to infect. Also, cirrosis as caused by alcoholism no longer need kill you. Quality of life worldwide would massively improve, and organ banks would always be able to fall back on the cybernetic versions.
The research to invent these things would be very expensive. Perhaps a corporation could be persuaded to invest for the royalties, which would assuredly be massive. Expenses would be recouped, one invention at a time.
I'd like to thank the Chinese Guy for inspiring this post.