I work in hollywood (editing television/movie trailers)... at least our agency is editing off of imacs. I can't speak for others but shared storage (Avid Nexis) is very costly. We transcode to proxy material, cut with proxies, and then uprez/conform to hd, uhd, etc. No one, at least I can't think of any agencies, editing higher than 1080p. Hell you even end up editing in lores super compressed mp4 for some projects.