They are missing what I think is the best box of them all the NVIDIA Shield.
Absent Amazon Prime, it is bit of a weak sister as it stands today. Going forward, it will continue to suffer from the absence of YouTube 4K support by decree.Once Amazon Prime comes to the Apple TV, I? would say that it is as good as it needs to be.
The Wired article suggested that the support isn't available in hardware for VP9 that is also used by Google TV for UHD. You can get other content in other formats but apparently all UHD content comes in VP9. We won't know if that's true until Apple comes out with something based on the A10X that is UHD capable (I suppose the same goes for the A11). The Roku, Fire TV and nVidia Shield all support VP9 in hardware.You tube 4K support could be done within the app if YouTube so desired.
Personally I don't see the need for a 4k hdr box. Unless you are invested in I tunes the tv should have the apps.