"Hey Siri" support and possibly wireless charging case alongside AirPower charging mat.
Apple's Ultra-Slim 12-Inch MacBook Air Rumored to Enter Mass Production in Early 2015
This information about the 12-inch MacBook Air provided by Digitimes lines up with previous reports, as Apple was rumored to be developing a new form factor complete with a buttonless trackpad and a fan-less cooling system for the laptop. Intel launched its new ultra low power Broadwell Core M processors this past November, which will likely power the 12-inch MacBook Air.
Aside from an ultra-slim design and a new processor, Apple will also look to offer the 12-inch MacBook Air in Silver, Gold, and Space Gray options when it launches in mid-2015.