So it only works in the TV app and iTunes? I wonder how long it will take devs to add it in their own apps. In the meantime I'll wait to upgrade.It does not in individual apps yet unless the apps are updated to change the color space. As of now they haven't been.
As the title says you are no longer forced to watch everything in 4k. Set the Apple TV to 4k SDR if you have a 4k HDR capable set and then Match Content for frame rate and dynamic range. This way SDR programming is played in SDR and the Apple TV will switch to correct frame rate and HDR or DV.