According to scooper Jeff Sneider on The Hot Mic, Jason Momoa will be back as Duncan Idaho for Dune Messiah when the project shoots this coming summer. This was a very safe bet, as everyone who knows the Dune story understands that Idaho has a key role in the story.
Although he fell defending Paul from the Sardukar in Dune Part One, allowing Paul and Jessica to escape to the Fremen, he returns in Messiah in the form of a ghola. This is basically a clone and is a gift for Paul from the Tleilaxu.
The story of Dune Messiah starts twelve years after the events of Dune Part Two. Mua Dhib’s jihad has grown beyond his ability to control it. Billions have died and entire planets have been laid waste to. Paul has failed to produce an heir with either Chani or Princess Irulan.
The Bene Gesserit, the Spacing Guild, and the Tleilaxu enter a conspiracy to dethrone him, by introducing the ghola Idaho to re-ignite Paul’s bond with Idaho therefore weakening his support among the Fremen.
Idaho is a major character in the events of Dune Messiah, which closes out the story of Paul Atreides and will also form an end to Denis Villeneuve’s Dune trilogy.
Timothee Chalamet will return as Paul Atreides alongside Zendaya as Chani, Florence Pugh as Princess Irulan, Anya Taylor-Joy as Alia Atreides, Javier Bardem as Stilgar, and Charlotte Rampling as Reverend Mother Mohiam.
Work has already started on pre-production for the sequel.