Holistic view of health, recovery and exercise - with Apple watch etc, Apple has all the data to say when you should be working out hard and when you should recover. Today, the only suggestion is to increase e.g work out minutes by 10% even if you worked out an hour a day...
Access to apple watch data for other training apps on the Apple TV, not just the "apple fitness service doesn't exist here, but I already use another service and cannot switch anyway (treadmill integration)"
Remove the apps from ios, so Apple doesn't think they need to wait a year to improve the apps... Deliver and update them separately and continuously.
Homekit - allow AppleTV to be a hub for other family members, not just the primary user of the AppleTV. Getting a homekit gadget working remotely via an AppleTV hub was impossible because my mother was the primary(only) user of the AppleTV and my father had added the homekit gadgets... Both members of the same iCloud family, obviously,
Allow AppleTV to handle siri requests for third party devices, don't require a home pod to do it. They've failed so miseably they aren't event available in most markets.