KGI Securities analyst Ming-Chi Kuo believes Apple is going to release at least three new products this year. Among them is an iPhone with a 6.1-inch LCD screen, second-generation AirPods and a MacBook Air laptop with a cheaper base price. No further predictions are made about the cheaper MacBook Air, but if it's real we can expect it in Q2 2018. This most likely points to a launch at Apple's WWDC in June.
Kuo doesn't offer any details on what to expect in an updated MacBook Air beyond a lower price tag, but the current models are certainly outdated as they haven't had any substantial updates in three years. Since that time, Apple has cut back on available models including a complete discontinuation of the 11-inch model. The only recent upgrade to the 13-inch model has been a bump to the base processor option last June, but it's still a Broadwell chip from the 2014–15 timeframe.
Aside from obvious internal upgrades like processors and graphics, another area that could see improvement is the display, as the MacBook Air currently offers a 1440 x 900 non-Retina display. We'll likely also see some USB-C/Thunderbolt 3 upgrades and perhaps an overall redesign given the age of the current design.