"Hey Siri" support and possibly wireless charging case alongside AirPower charging mat.
AirPods and AirPower: Everything We Know
Panther: User at the Center
According to the article, the theme behind the upgrade will be putting the "User at the Center" of the OS.
They said User at the Center features will make it simpler for individual users to personalize their computing experience and to move seamlessly among Macs and other devices
eWeek fills in some details on previously mentioned features coming to Panther, including Multiple Graphical Logins, Piles, new file system format akin to BeOS's, and rumors that Panther will provide 64-bit support.