Apple is apparently planning on updating the MacBook Air lineup during the third quarter of 2013 with new Intel processors and a Retina Display. Component makers speaking anonymously claimed Apple will use Intel's Haswell chip platform in the new MacBook Air, and that the upgrade may include additional external features, too.
Sources told (English translation) China's Economic Times parts suppliers will start shipping components to Apple manufacturing partner Quants during the second quarter and that the company is planning on sticking with the current 11-inch and 13-inch screen sizes.
Assuming the reports are correct, it sounds like a fall Retina MacBook Air launch is coming, although that doesn't rule out the possibility of an interim update with performance improvements.
Apple is sticking true to form and hasn't commented on the Economic Times report.
[Thanks to Macotakara for the heads up]