I don't think the Air will exist much longer. They aren't going to keep the Air around long term when they have a 12 inch MacBook that is thinner and lighter. The Air will be phased out in 2 years or less. They will keep it around like they do the cMBP but it won't be redesigned or updated internally.
Apple will have the 12 inch Macbook for the Ultra Portable user's and a 13 and 15 inch pro for everyone else. They will bring the pricing of the 12 MB down to take the place of the Air's sub 1,000 price point. Pricing will probably look something like:
Base model 12 inch MB-$899-999 and up.
Base model 13 inch rMBP-$1199-1299 and up.
Base model 15 inch rMBP-$1899-1999 and up.
I love the Air and hope I am wrong but I just see the Air going the way of the cMBP.