whoa, that'd be pretty crazy! You'd have to change out the screen assembly completely though, since the macbook air used an LED screen and all the iBooks are CCFL.
I'm sure there's a way to do it, but it's probably not a good first mod if you don't have too much experience. But, if you have the cash and time, go for it- I'd love to see it when it's done! I do love those old iBooks.