I want to be able to close my eyes, disconnect all of my 5-10 senses and plug them into a computer generated world where the rules are as I define them. So I could be lying in bed yet genuinely feel that I am running a marathon.
http://wiki.bmezine.com/index.php/Magnetic_Implant
http://www.wired.com/gadgets/mods/news/2006/06/71087
Of course it didn't go well in the long term, but it's a very interesting experiment. Here is the article about how it went wrong (contains some graphic imagery):
http://news.bmezine.com/2006/04/01/another-two-months-of-mag...
It's all wishful thinking though. There are serious disadvantages to putting hardware in bodies. Upgrading or fixing broken implants would require surgery, which is risky and expensive.
I would be more interested in a way to capture and interpret the raw visual information from the eye(s) before it gets processed by the brain. Perhaps the optic nerve would be an ideal spot to capture such information. I presume that there would also be great difficulties in this endeavor, not the least of which being the fact that everyone's individual "format" of visual information (the exact distribution of rods and cones, pathways of nerves, etc.) would likely be too different to make the production of digital circuitry feasible.