Apple has published a new support page explaining the ins and outs of these updated standards in the iTunes Store:
You can buy or rent movies from the iTunes Store in high-definition (HD) or 4K resolution formats. These videos might also feature high dynamic range (HDR) or Dolby Vision.
When you buy or rent a movie from the iTunes Store, it automatically plays in the highest-quality format available for the device on which you’re watching it.
That works for me. I have a 1080 TV, so why use bandwidth I don’t need to? This, however, does bug me:
You can download a local copy of an HD movie, and you might be able to download HDR and Dolby Vision versions, but you can’t download a 4K version.
I assume this is some sort of licensing thing, but I don’t like it. If I pay for something, I want it taking up space on my home media server. If I buy a new TV, I could stream previously-purchased movies in 4K, but I can’t play them offline unless I download the 1080 versions.