Pretty much all of it is necessary for flight in the era of integrated modular avionics, even the brakes are partially implemented in that room.
Entertainment might have main content distribution server there, as well as gateway between flight systems and entertainment (how you get current flight info and stuff like plane cameras)
I'm truly mindblown because of such a waste of luggage space, of general space, and of electronics. In recent years airlines have started to charge even for the small handbag fitted under the seat, while packing even more obsolete eletronics into it. I guess the lobbying of copyright, media, and entertainment industries simply prevails everything including reason and safety.
Are there really airlines that have both seatback screens and also charge for a small bag that can go under the seat? At least among US airlines, those two things are generally mutually exclusive.
That's rather my collective experience. Cannot tell if a certain airline is simultanously having headrest entertainment system and charges extra for the little luggage. I'm certain though that easyjet and ryanair tightened spaces between the rows and were putting printed ads on the headrests, 40-50cm in front of almost every passenger's eyeballs.
Entertainment might have main content distribution server there, as well as gateway between flight systems and entertainment (how you get current flight info and stuff like plane cameras)