Seems like they would want to focus on the dark MAX first to harmonize that fleet, then move on to the dark 737NGs so all 737 have some form of seatback entertainment, then the 753s since that's a small fleet and flies some loooong flights, THEN go on to tackle the huge dark Airbus fleet. But instead it looks like they're going for the additional years of confusion route. I'm sure it has to do with heavy checks and ease of dealing with some of the parked Airbuses though.