"Hey Siri" support and possibly wireless charging case alongside AirPower charging mat.
AirPods and AirPower: Everything We Know
Apple Seeds First Beta of iOS 11.4 to Developers [Updated]
Registered developers can download the new iOS 11.4 beta from Apple's Developer Center or over-the-air once the proper configuration profile has been installed from the Developer Center. It appears there's currently a bug preventing the beta profile from being downloaded, but it should be addressed soon.
It's not yet clear what new features will be included in the iOS 11.4 beta aside from the new ClassKit framework Apple introduced at its March event, but we are waiting on several features to be added to iOS 11, including iCloud Messages and AirPlay 2, functionality that has popped up in previous betas and then disappeared before release.
We don't yet know if any of these features will be introduced in iOS 11.4, but we'll update this post once we download the beta and discover what's new.
What's new in iOS 11.4 Beta 1: Messages on iCloud is present in the iOS 11.4 beta after being removed from iOS 11.3 ahead of its release, as are AirPlay 2 features. Apple TV devices are once again listed in the Home app, an AirPlay 2 option.
Stereo support for the HomePod is included, but the feature doesn't work properly as it requires unreleased HomePod software.