We've been banging on about the possibility of a new MacBook Air for some time, but we think that late 2018 will be the time for a new model.
We'd expect a new MacBook Air to now to launch at Apple's September event featuring either Intel's third iteration of its Skylake microarchitecture, known as Whiskey Lake or the previous iteration (Kaby Lake refresh) chips.
Economic Daily News suggests the launch will come too early for Whiskey Lake chips, but their launch date is uncertain so we'll say the jury's out on that.
It's worth noting that we don't really know whether the MacBook Air name will remain - it's highly possible that Apple could re-form the lower rungs of its notebook offering and simply release a larger MacBook instead of a new Air.
It's Intel's fault that there's a bit of uncertainty about timing; Intel's actually-new next proper generation of processors will debut in mid-to-late 2019 (possibly announced at Computex in June 2019) and has been delayed in favour of refinements to the previous microarchitecture. The problem, says Intel, is yield - the number of saleable chips Intel can produce. With a new microarchitecture, it's harder to make chips to begin with.
The Canon Lake microarchitecture will feature a change to the manufacturing process from 14nm to 10nm and will offer significant efficiency improvements. The delay is problematic for many manufacturers. For Apple's part we're expecting a new Mac Pro in 2019 and surely the plan for that would have been to use Canon Lake 10nm Intel Xeon processors.
Canon Lake also makes it likely that we'll see refreshes of the processors inside all Macs late next year anyway - even if we do get a new MacBook Air replacement this year.