I highly doubt a $999 MBA will happen... it doesn't make good marketing sense. If it were to happen, it would have to be a severely underpowered computer, as to not steal every sale from the 13" macbook and 13" MBP.
I bet we'll get an MBA with similar specs as the base 13" MBP now, but a few hundred dollars more in price... think $1499 for the 'base' model (2gb ram, about 2.26ghz). THen I would expect a high-end with 4gb, 128 or 256gb SSD, and around 2.5ghz for $1999 or above. I think that would make the most sense for apple and for us. Apple would hate for MBA sales to be 'poached' from their other models. I bet you'll get good specs, but for a few hundred dollars more than a comparable MB or MBP.