I have implemented a video skill (still in development). I was able to enable the skill successfully. Devices were discovered correctly as well. I picked one of the discovered devices and I linked it to my Echo Show. However, when giving the command "Watch [ChannelName]", the response tells me to go to Settings -> TV & Video to set it up. When I navigate to the TV & Video setting, I can see my video skill enabled and my echo show linked to the discovered device.
In my previous experience, when I say "Watch [ChannelName]", Alexa implicitly route this command to the device I linked my Echo Show with.
Note*: When I tried with a different account, the above issue does not exist. I am not sure if this is Alexa account specific.