Backlit Keyboard backward compatible

Very much doubt it.

I don't know. All the keyboard has is probably some kind of LED array and a single ribbon connection to the motherboard. Seeing as how the keyboard isn't any different (with the exception of low opacity letters), it shouldn't be more than a hop / skip / jump from the previous model.

If anything, it would be impractical installing due to the bottom up design of the MBA. Literally everything would have to come out.

I too am interested in actually VERIFYING the validity of it, and I'm sure someone who can brave the loss will head this endeavor. When that is, however, is a completely different question.