We'll find out when the next Apple TV is announced shortly. If AV1 isn't there people should worry. Apple was using HEVC in the iPhone 6, so they aren't scared to be early on this stuff.
Whether or not Apple TV has AV1 out of the box won't matter (although it would be nice).
If Netflix or YouTube want AV1 on Apple TV then they'll just implement it in their applications. Netflix has already implemented AV1 as an option in their Android application:
