FWIW I've given up on a dedicated device for that use case; my 11" ultrabook-like (Samsung NP900X1B) can play a much wider range of videos (and also games, coding etc.) and is small enough to be comfortable on a plane. There's a very small space where I'd want a 7-inch-type device (on my way to/from a club is pretty much the only use case I can think of), but I'm not sure there are 7-inch screens much better than a big phone screen.

(personal experience, probably different for other people)