Seeing as you have the eye tracking you could probably greatly reduce the FPS/bitrate of windows that are out of gaze. This kind of foveated rendering seems to

Seeing as you have the eye tracking you could probably greatly reduce the FPS/bitrate of windows that are out of gaze. This kind of foveated rendering seems to already be used in their ecosystem so I assume its sufficiently slick for Apple. Apps will sleep when not being gazed and such. This allows you to restrict full bitrate to a single window with a maximum resolution and keep the user experience high and astonishment low.