Update March 24, 2017: Apple has released an updated version of iTunes 12.6 that removes a mysterious "Show on Profile Page" toggle switch that was appearing in playlist edit screens.
Apple has released iTunes 12.6 which introduces a change to movie rentals, while also offering performance improvements. With this update, users of devices running the upcoming iOS 10.3 for iPhone and iPad and tvOS 10.2 for Apple TV will be able to watch their iTunes movie rentals on any of their devices.
Rent once, watch anywhere. Now you can enjoy your iTunes movie rentals across your devices with iOS 10.3 or tvOS 10.2. This update also includes minor app and performance improvements.
Apple hasn't given a release date, though this iTunes update may indicate that it's close at hand.
You can download the latest version of iTunes from the Updates section of the Mac App Store.