"Hey Siri" support and possibly wireless charging case alongside AirPower charging mat.
Apple Seeds Potential Golden Master Mac OS X 10.6.6 Build 10J537 to Developers
Apple today seeded a new version of Mac OS X 10.6.6, known as Build 10J537, to developers. The update comes four weeks after the initial developer build was seeded to developers even before Mac OS X 10.6.5 saw its public release.
Interestingly, we've been told that the new build is being listed as a golden master version for those accessing it through the Mac App Store developer program. The designation would suggest that Apple is preparing to release this version to the public in the near future. The listing for regular Mac developers not participating in the Mac App Store aspect of the program appears, however, to not carry any mention of it being a golden master build.
Mac OS X 10.6.6 Build 10J537 offers "developer support for fetching and renewing App Store receipts" and the seed notes ask developers to focus their testing efforts on Bonjour, Dock, OpenGL, Printing and Spotlight. The build weighs in at 1000 MB as a combo update.