This isn’t a situation of outright replacement so much as a situation where James Cameron was set to direct what has been described as “a passion project” (I feel like Cameron doesn’t have any other kind), but has since moved away from such direct involvement and hired someone to bring the story to life anyway. And what is that story? THE DIVE deals with the true tale of “two pre-eminent free-divers [Francisco “Pipin” Ferreras and his wife Audrey Mestre] who, with but a breath of air in their lungs, plunged to unimaginable depths before swimming back to the surface. Mestre died during an attempt to better her world record to 557.7 feet.”
I’m not quite sure how screenwriter J. Michael Straczynski (“Babylon 5”) will stretch things out to fill a full movie, but the research I’ve done reveals that there is a fair amount of possible back story to the relationship of Ferreras and Mestre specifically with allegations of abuse and violent jealousy tainting their love.
Cameron filmed Ferreras via submersible when he did a tribute dive to his late wife by plunging to the depth that ended up killing her. No release date (or shoot start date) has yet been set.