Even if they do update the 13" with Skylake, I doubt they would ever put a retina display in it. It would cannibalize the MB, and they would never ever want to do that. They would keep that awful TN panel to encourage people to go for the MacBook. They simply aren't going to jeopardize the health of their future mainstream consumer notebook by keeping the MBA up to date. It would also encourage people to use ports that Apple wants to get rid of, like USB-A, which is no good in their eyes.
The MBA increasingly has no place anyways, especially since the next MBP is rumored to be thinner than it. So, I bet that Apple is either going to do nothing, which I think is likely, or they will do the least amount of work possible while using up the old display panels at the same time. Remember, this is the company that is willing to sell their 15" professional geared notebook with CPU's that are two generations old. If they think this is okay, they won't blink at selling the MBA with Broadwell until they discontinue it sometime in the early 2020's. (It's going to be the next 2012 cMBP I think).