"Hey Siri" support and possibly wireless charging case alongside AirPower charging mat.
AirPods and AirPower: Everything We Know
Apple Releases Second OS X 10.11.4 El Capitan Beta to Public Beta Testers
The second beta is available through the Software Update mechanism in the Mac App Store for those who are enrolled in Apple's beta testing program. Those wishing to join the program can sign up on Apple's beta testing website.
OS X 10.11.4 includes a couple of new features, such as the ability to support password protected notes in the Notes app, but like the recent OS X 10.11.3 update, it appears to focus primarily on under-the-hood bug fixes and performance improvements with few noticeable outward-facing changes.
Apple is likely to release OS X 10.11.4 in the spring, alongside iOS 9.3, watchOS 2.2, and tvOS 9.2.