Simply moving to an IPS non-Retina screen would make more sense.
The current Air resolution is not that bad, but color reproduction and viewing angles are pretty bad for a product of its price.
Apple would'nt put a higher resolution in Airs unless they go Retina as there is no proper way of scaling things in OS X without pixel doubling, and stuff would get way too small.
There's a couple problems I see with a Retina Air:
1. Reduced margin.
2. Either reduced battery life or thicker chassis, unless some sort magic is done to reduce internal component size even more.
3. Cannibalization of the 13" rMBP, which would be almost the same computer.
I think the MBA will go Retina someday, but not this early.
----------
So you would have to somehow make the keyboard smaller if you want to reduce the bezel size.
Not necessarily, the 13" rMBP has a smaller bezel than the MBA yet it has the same screen and keyboard size.
I think the issue is more with the the thickness of the display panel. You couldn't get that tapered effect if you reduced bezel size since the panel wouldn't fit in the extremities of the top lid, thus ruining the optical illusion that makes the Air look thinner than it actually is.