I personally think that a set that could top the Millennium Falcon is highly unlikely, but there is a slim chance. After all we got the Harry Potter Hogwarts Castle (71043) which almost beat the Falcon in 2018. It would definitely have to be a licensed set to be as popular as the Millennium Falcon, so Star Wars, Harry Potter, LEGO Movie 2, Ninjago, DC, Marvel, and Overwatch could all be contending themes. I honestly would like the set not to be Star Wars for we already have lots of big sets from Star Wars. But Star Wars is the theme with the most items to make into a big set. I think that a Triwizard Tournament set for Harry Potter could be a giant set that could top the Falcon. It could include many of the different tasks of the tournament, but I think the most likely would be the maze. The set could include the maze itself, all of the monsters that the contestants have to face, minifigures of Harry Potter, Cedrid Digory, Victor Krum, and Fleur Delacour, and the portly that brings Harry and Cedrid to the graveyard where they confront Lord Voldemort. I think this could be a massive set if thought through well.