Obviously it would be impossible to adapt all of Christie’s stories as part of the same film series, but depending on how critically and commercially Death on the Nile is, perhaps Fox would be willing to expand the focus past Poirot.
Along with the mustachioed detective Hercule Poirot, Agatha Christie’s other popular starring characters included Miss Marple and the duo Tommy and Tuppence.
That could simply be through telling these other Christie stories as self-contained movies with only passing references to other areas of this “universe” or even having Poirot cross paths with these other characters.
It’s important to mention that Kenneth Branagh hasn’t run this idea past any 20th Century Fox bigwigs yet, but as he said later while speaking with AP, he bets “they’ve been thinking about it.”