"Hey Siri" support and possibly wireless charging case alongside AirPower charging mat.
AirPods and AirPower: Everything We Know
Mac OS X 10.5.5 Build 9F13 Seeded
This new version (Build 9F13) details 10 more bug fixes and unlike prior builds, Apple lists no known issues.
It's difficult to predict when the next version of Mac OS X will be released to the public, but it should be a free upgrade and include a number of bug fixes.