The mobile Haswell chips don't seem to be likely to appear until the fall. I think the Macbook Air will see a redesign, as Apple usually does this after 3 updates of the same design. We have had 3 different unibody Airs, so it is due.
I don't expect much, except a smaller footprint and IPS display. We may also see the black finish that the iPhone/iPad Mini have come to the Air which could look cool.
Don't expect Retina, the battery in the Macbook Air can't sustain it.