But Fincher's is not the only 20,000 Leagues modernization in the works. Fox is in pre-production on another one -- gotta love the public domain -- with Ridley and Tony Scott, who are in negotiations with Wanted's Timur Bekmambetov to direct. Fox's film is set in the future, but is otherwise reasonably faithful to the novel, according to the Hollywood Reporter.
I think Bekmambetov is an interesting and very promising filmmaker -- he's made big-budget films with an edgy, off-kilter bent. Both Wanted and the Watch series, which he made in Russia, had an aggressively absurdist streak that was fascinating even if the films didn't quite hold up. That said, I don't know how he wouldn't mangle Jules Verne, whose sincere, wide-eyed storytelling makes up much of his charm. On the other hand, Fincher in Benjamin Button mode seems like the perfect choice for the material.
In any case, I'm not sure if it's possible for two separate adaptations to proceed simultaneously -- one would have to transform into something else. It's worth noting that the Fox project is in the early stages of development, and hasn't been greenlit yet. But I am generally in favor of more Verne adaptations, at least so long as they don't end up like the weirdly boring Journey to the Center of the Earth from two years ago. Or like the Jackie Chan version of Around the World in 80 Days. Someone do this right for God's sake.