iTunes is clearly showing listing certain movies as 4K and HDR in users’ purchase history, as reported by MacRumors. Users are limited to 720p and 1080p downloads at the moment, but Apple seems to be adding the new tags to prepare for a 4K rollout soon.
That the tags are showing up publicly is likely a mistake; something similar happened with Google Play Movies last year.
My bet is we’ll hear more about 4K during Apple’s imminent iPhone 8 event in the next few months. It’s about time.