The ATV4 doesn't support HDR...
Also, anyone who happens to be in the market for a TV is going to be getting a 4K model or a low-end budget piece of junk. 4K TVs are the standard now, regardless of how much or how little the benefit over 1080p. Technology and the market have moved on.
The benefits of 4K are negligible to the average viewer whereas HDR will be visible and benefit everyone. And in order to be a panel that supports HDR it has to have throaty set of specs to begin with. My point is that no one should be fighting for a 4K Apple TV, it's the wrong battle. HDR, different story.
And short term with so little 4K or HDR content available and all of it on services free and bundled with all new TV's, a 1080 ATV4 is all anyone needs right now. I understand why Apple must update the product to keep up appearances but in reality it isn't going to change anyone's life right now unless they sit 3 feet away from a 65 inch TV purchased within the last year. It's not a rational use case.