Another big missing feature is frame rate matching. The Apple TV 4K recently added an option to match the frame rate of the output to that of the content, so 24fps content is output at exactly 24fps. This is something blu-ray players have done for many years, and it makes an enormous difference. Once you're used to it, there's no going back.
Of all the apps I use on my Apple TV 4K the only one which doesn't support this feature is... can you guess?
The Now TV Apple TV app is driving me crazy. Would love support for the TV app and ideally have a full version of the Now TV app with at least my to watch list and recently watched/resume. Seems crazy that the iOS app has everything but the one for Apple TV doesn't. Almost makes me want to cancel my subscription and stick to all the stuff that is intergrated properly.