"Hey Siri" support and possibly wireless charging case alongside AirPower charging mat.
AirPods and AirPower: Everything We Know
Apple Seeds First Beta of iOS 9.2.1 to Developers
The iOS 9.2.1 beta is available for download immediately from the Apple Developer Center, and a public beta will likely be available in the near future.
We don't know what changes iOS 9.2.1 will bring to iOS 9, but as a minor .1 update, it's likely to focus on performance improvements and fixes for bugs that have been discovered since the release of iOS 9.2. We will update this post with any changes that are discovered in the latest beta.
Update: Apple today published a support document addressing some issues with Mobile Device Management on iOS 9.2. When installing an app on iOS 9.2, some apps don't finish the full installation process.
According to the support document, a bug fix is coming in the near future, and it's likely the iOS 9.2.1 update resolves the problem.