"Hey Siri" support and possibly wireless charging case alongside AirPower charging mat.
Apple Seeds First Beta of iOS 10.2.1 to Developers
Registered developers can download the new iOS 10.2.1 beta from the Apple Developer Center or over-the-air with the proper configuration profile installed.
It's not yet clear what features are included in iOS 10.2.1, but as a minor 10.2.x update, it's likely to focus on bug fixes and performance improvements rather than major outward-facing changes.
iOS 10.2.1 comes shortly after the release of iOS 10.2, a major update that brought new emoji, the TV app, new Messages Screen Effects, Music improvements, and a whole slew of bug fixes.