Dune 3: Electric Boogaloo.

They probably would name it after the next novel, "Dune Messiah."

I think the next book covered the events after Paul became emperor and the fallout that ensued from that. Many of the noble houses were angry over Paul upsetting the balance of power in the known universe and he had to fight back and bring them under his control. He also made Arakkis the capital of the empire and banished the Corrinos (the previous imperial family, though Princess Irulan stayed with him as his official wife) to the very moon where they trained their Sardukaar soldiers. Much of the drama in this book and the next one involved various factions plotting to kill Paul and his family off, as well as the different noble houses' reactions to this new emperor that was also worshiped as a god.

I think Villeneuve is also going to include some of the events from "Children of Dune" in the third film as well, because the events surrounding the birth of Paul's twin children was quite shocking too.