Look at MacRumors and other sites, it seems tvOS 14 will be a bit more major than usual:
Home Screen:
- Persistent AirPlay 2 audio output
- Customizable Watch Now page, hopefully we will be able to not only filter but reorder (I want My Channels at the top)
- Workouts app for yoga and other indoor fitness activities
- ScreenTime and Kids profile
Home Screen:
- Organized into 3 sections: Play (games and Apple Arcade), Video (TV and other streaming apps), and Apps (Photos and other apps)
- Apple Arcade app similar to Apple TV app, which sandboxes all the Apple Arcade games
- Offload Unused Games
- Support for more than 2 gaming controllers
- Battery status for more gaming controllers
- Smart Video and Audio Settings for HomeKit TVs, automatically setting optimal video and audio settings
- Calibrate app for tweaking TV settings, ideally using iPhone as the calibrator (similar to THX tune-up app)
- Improved 4K Upscaler similar to nVidia Shield
- Support for AV1 codec (e.g., YouTube in 4K)
- Home app for HomeKit