Apple has released the third betas of iOS 11.3 and tvOS 11.3 to registered developers. While iOS 11.3 adds a few interesting new features, the third beta seems to mostly consist of bug fixes and relatively minor improvements, following the introduction of the battery health feature in iOS 11.3 beta 2, although iOS 11.3 beta 3 is also now available for the sixth-generation iPod touch, which was excluded from the two prior betas. It is likely that updated public beta versions will also appear in the next day or two.
Update: MacRumors reports, and we’ve also confirmed, that the third beta of iOS 11.3 also removes support for AirPlay 2 and the Apple TV entry in the Apple Home app. The release notes make no mention of this, so it’s unclear whether these are coming back in a future iOS 11.3 beta or will be pushed off to a later release.