"Hey Siri" support and possibly wireless charging case alongside AirPower charging mat.
AirPods and AirPower: Everything We Know
Another Day, Another Panther Build (7B59 and 10.2.8)
Of interest, beyond Panther Client, Apple has also seeded Mac OS X 10.2.8 -- which replaces the previous 10.2.7 seeds. ("Note: the version number has changed, this previously was seeded as 10.2.7 6Rxx). This latest version of Jaguar contains improved functionality and reliability for Audio, Bluetooth, Classic, Finder, Graphics, LDAP, Power Management, Safari, Firewire Devices, as well as security updates.
The current PowerMac G5s ship with a version of Mac OS X 10.2.7 (builds 6Sxx).