"Hey Siri" support and possibly wireless charging case alongside AirPower charging mat.
AirPods and AirPower: Everything We Know
NVIDIA-based MacBook Airs Now Shipping
The new MacBook Air uses the new NVIDIA-chipset which includes the GeForce 9400M graphics processing unit (GPU). This improved GPU hardware should provide much faster graphics performance for Apple's thinnest laptop. In addition, the new MacBook Air should also see the same improvements in h.264 playback that we've seen in the new MacBooks and MacBook Pros. There had been evidence that Apple now supports h.264 hardware accelerated decoding on the GeForce 9400M.
The offloading of processing from the CPU to the GPU will likely be more dramatic for the MacBook Air since its CPU runs slower (1.6-1.8GHz) than those of the MacBook and MacBook Pro.