On current domestic flights the flight door hinges are 2 inches from bathroom hinges. So if there's now the need for two doors (an airlock) will they be lengthening the plane 3 feet to allow for this?
Some (all?) U.S. domestic airlines currently have this exact system in place, except with a flight attendant standing guard between the first row of seats and the galley/lavatory/cockpit, starting just before the pilot opens the cockpit door. I have no idea if this has been a regulation thing or just a thing I notice the airlines I fly do, but this physical barrier would probably follow the same usage pattern as the current meat-based barrier.
That already sounds more complex than a door IMO