To make a long story short; it is planned for the future. The problem is not that you can’t do it. You very much can. Just go into the inputmap for the AppleTV remote and add it. But as you will notice is that you will change the volume when you are not playing video as well. And that is the main issue at the moment. All button presses are global and not contextual. So what the devs have on their radar to do is to make sure that a certain keypress on a certain remote is only reacting a certain way depending on where in PMP the user is.
It will be done, but it is not done over night.
