June or July: Highly unlikely.
August or September: Slightly more likely.
October or November: Best Guess.
December: Not at all likely during the Holiday buying season.
Next January MWSF: If they don't decide to do it in the late summer or fall, or if Intel is slow on getting them a faster than 1.8 to bump the CPU. Also realize that it may end up waiting for a new chipset. Not sure if it is running on a modified Napa or Santa Rosa (current MBs and MBPs run Santa Rosa), and Montevino is due out this fall, but the MBA will probably be the last to see it. It is a special case in itself and if it isn't running SR now, then I couldn't tell you much more without knowing more.