There is most likely extensive damage now due to taking the interface out, so there might not be enough neural substance to attach anything to anymore.
> Did the system damage his visual system in his brain?
I know of no working system that attaches directly to the optic nerve, and the article is very light on details. I assume these implants worked by projecting light on retina remnants. In cases where the eye is destroyed but some of the light-sensing apparatus is still intact, there is the potential for a device that sends light directly into the remaining rods and cones.
This is different from a direct electrical interface, which remains the holy grail of brain-machine interfaces.
I doubt they would have removed the Microelectrode arrays from the brain, that would have caused serious damage as the MEAs would be encapsulated in glial scar tissue. The article made it sound like they just removed the two jacks from his skull.
The devices were probably Utah Microelectrode Arrays(MEAs) the MEAs were no doubt implanted on the visual cortex on the cerebral cortex to induce phospehnes.
This is no holy grail, and MEAs have provided computer-brain interfaces since the 80's.
check out my other comments in the thread for more information
I don't think he means that it is technically impossible, just that before he had hope and an opportunity, and now the opportunity is gone and there is no other one like it.
Why was the first time non-permanent while the second time was? Did the system damage his visual system in his brain?