I wouldn't be surprised at all if Apple kept the base configuration at 2 GB RAM. Judging from the iMac refresh, I predict not only will the RAM stay the same, the SSD sizes will as well. SSD prices haven't dropped at all enough.
However, we'll get the bump up in processor, thunderbolt tech, and likely an HD Facetime cam.
I'm hoping for improved battery life too?
We'll most probably see CPU bumps, facetime HD and a boost to the graphics. I doubt we'll even see Thunderbolt seen as how thin the MBA is... and also, they don't have firewire ports on the current gens (even the white macbooks dont have firewire). I think they will push Thunderbolt as a pro feature... hope im wrong though
We've bought two of the 13 inch Air's with 4gb in stores; one in WA and the other in HI. It's not a problem to find them, if you're willing to accept the 256gb SSD.