I dont see that happening for a long while. At the moment, the market for the Airs (non pros) dont care about the high res screen. Personally, I think the current Air's screens are great as is.
There's no reason for it, really. The Airs need to stay cheap for as long as possible. That and the 13" Pro and Air are already blurring together..that screen needs to stay on the Pro line to differentiate beyond body styles.
Update the Air's body (which in itself doesnt need, because it still looks amazing) if they need to, update the internals..etc. Hell, a higher res (non-retina) screen might be in the cards, but IMO Retina is off the table for the Air line.
/armchairspeculation