LOL. Yeah, at this point I have to imagine that since similar lag is being seen on 13" rMBP, that this problem does not necessarily come down to a lack of horsepower and that it is fixable in software. So those rMB owners who are suffering from lag today may eventually get a fix. The Air screen, however, is most definitely not fixable in software.I tried to convince myself the 2015 MBA I had was superior to the MacBook because of the ports and processor but that screen, my God. I returned it 3 days after I bought it. Its embarrassing Apple still sells a new MacBook in 2015 with that horrid TN display, much less what they charge for it. I'll gladly put up with a split second lag to never have to look at that MBA display again.
Even if they have no plans of ever updating the Air line to use "Retina" (HiDPI) and will likely retire it and replace it with the rMB at some point, you'd think they would at least replace the panels in the Airs with IPS ones that match the DPI of the current TN panels. (It would not be unprecedented for Apple to use a non-Retina IPS panel in a portable product: Exhibit A is the iPad 1.)
-- Nathan