I think the 4th film will deal with the O'Connells dealing with the Incan mummies since the end of film 3 did say that Incan Mummies were discovered in Brazil. I think film 4 will deal with Johnathan living a rather quiet life in Brazil, until an ancient from the Aztec times rises from the dead which is even more brutal than any Mummy that Rick and Evelyn have ever faced since it has the ability of telepathic manipulation and telekinesis. Ardeth Bay reunites with the O' Connells since his absence is explained as being on a expedition in Europe for more undead mummies.