Do any trailers support HDR?
on itunes? Unlikely. In general? Unsure, but first and foremost you'd need a delivery platform capable of HDR.
FWIW, I looked through my collection (~200 movies) and the only surprising movie (pre-late 00s) to show up in 4K was Ghostbusters 1984.
Hoping for new files down the road for catalog titles that we know are in 4K (Bond, Casablanca, etc)