I have an “old” Apple TV 4K without Thread support.
Is it beneficial to have support with HA or will Thread be supported anyway.
Another reason to upgrade would be better responsiveness from HomeKit as it has more performance.
What do you think?
There are now 3 generations of “Apple TV 4K”. Do you have the first or the second? The second (2021) supports Thread. The first does not. If you have original 4K, the new one might be a decent upgrade for you because of the upgraded specs alone. You may already know this, but only the more expensive model supports Thread. If you have the second generation, it’s probably not worth it. Although having said that, I am upgrading one of mine anyway. 
As far as Thread and HA, the Apple TV with Thread support is not going to do anything for you to add Thread to HA. I think you need separate hardware for that. But I think what it will do is help extend your Thread network. So it could be somewhat beneficial.
Thanks for that. I have a 2021 model.
I am wondering if it is quicker for HomeKit but I guess I will keep the one I have for now.
Maybe you can report here once you receive your new Apple TV.