"Hey Siri" support and possibly wireless charging case alongside AirPower charging mat.
Apple Seeds Sixth Beta of iOS 10.3.3 to Developers and Public Beta Testers
Registered developers can download iOS 10.3.3 beta 6 from the Apple Developer Center or over-the-air with the proper configuration profile installed. Public beta testers can also download the beta over-the-air after installing the configuration profile.
There were no significant features or notable bug fixes found in the first five iOS 10.3.3 betas, suggesting iOS 10.3.3 is an update that's minor in scale, focusing primarily on security updates, bug fixes, and other small improvements.
iOS 10.3.3 is likely to be one of the last updates to the iOS 10 operating system, as Apple has shifted development to iOS 11. The first beta of iOS 11 was released to developers on June 5 following Apple's Worldwide Developers Conference keynote, and two betas have been seeded so far.