"Hey Siri" support and possibly wireless charging case alongside AirPower charging mat.
Apple Seeds Sixth OS X 10.10.3 Yosemite Beta to Developers, Public Beta Testers
The new beta, build 14D127a, is available for registered developers through the Software Update mechanism in the Mac App Store and through the Mac Developer Center. OS X Yosemite Recovery Update 1.0 is also available, improving the reliability of Yosemite Recovery when restoring from a Time Machine backup.
OS X 10.10.3 includes several new features, like the Photos for OS X app. Designed to integrate with iCloud Photo Library and the Photos app on iOS, the Photos for OS X app is a replacement for both iPhoto and Aperture. Reviews have suggested that while Photos is a suitable replacement for iPhoto, with more advanced tools and performance optimizations, it may leave professional users disappointed in its initial incarnation.
Along with the new Photos for OS X app, earlier OS X 10.10.3 betas have introduced a redesigned emoji picker that consolidates emoji into a single scrollable page with clear labels, new diversified emoji and emoji skin tone modifiers, new flag emoji and updated emoji for the iPhone, iMac, and Apple Watch, and support for Google 2-step verification when setting up accounts in System Preferences.
With the fifth OS X 10.10.3 beta, there were just two minor bug fixes to the OS X Photos app, and today's update likely includes similar small changes. Given that we're on the sixth beta, OS X 10.10.3 is undoubtedly getting close to completion and we may see a public release of the software in the near future.