"Hey Siri" support and possibly wireless charging case alongside AirPower charging mat.
AirPods and AirPower: Everything We Know
Apple Seeds Second Beta of iOS 9.2.1 to Developers and Public Beta Testers
The second iOS 9.2.1 beta, build 13D14, is available as an over-the-air update for those who downloaded the first beta and it's also available from the Apple Developer Center.
It is not yet clear what changes iOS 9.2.1 will bring to iOS 9, but as it's a minor .1 update, it's likely to focus on performance improvements and introduce fixes for bugs that have been discovered since the release of iOS 9.2. No significant changes were discovered in the first beta, but we'll update this post if anything new is unearthed.