I don't think it would be worth trying to repair the key because it is actually damaged, not just worn. It is hard (impossible) to see in the picture, but it is not just the ink that is missing. Its almost like a layer of plastic has been removed somehow. It sort of looks like there used to be clear coat that has peeled off in the center of the key. That is not what actually happened, but it is the best way I can explain it. I would need to resurface the key, then get it etched. Then, of course, I would have to laser etch the other keys...
I think I will just bide my time and wait for a good replacement.