The MCU is in an interesting place after Avengers: Endgame. For the first decade of the project, almost every film was slowly building to the arrival of Thanos, but with that threat dealt with, what's next? Well, there are a number of competing theories as to who the next big bad will be, with the smart money being on Galactus turning up at some point. But now fans think a very subtle reference in Endgame might point the way forward.