Do you really need autocomplete to type rating:s rating:q rating:e?
order: status: can be done easily but sub: fav: I wouldn't bet on if it can't query the userlist in a simple fashion. The rest are essentially worthless in autocomplete.
Well, maybe you're right about the rating: being unnecessary, and most of them are indeed worthless in autocomplete, but user:, fav:, sub:, and especially order: and status: would be convenient.
Maybe it seems worse to me because before DanbooruUp Firefox would autocomplete these when I searched, so I dunno, maybe it was a stupid idea.