I would be interested if Apple brought that back, but I highly doubt they will especially since the Air covers there most basic "casual" computing market. The sales pitch would be something like:
"Hey! Who wants a laptop that's not as powerful as the Pro and not as portable or great on battery life as the Air? Anyone??"
I wouldn't call the base Air a good computer for casual computing, a 1.3GHz (sure, there's turbo boost) i5 low voltage processor can't go that far, though. Probably will be obsolete in the next couple years. Now the 1.7GHz is more along the lines of something good for me, but I won't be buying an Air until they decide to let it have the 16GB RAM it really could use, so that it is even more future proof. But until that day, I'm gonna stay on my 2GHz Late '08. 8GB RAM really helps the thing.