According to Deadline, "Conquest" is now in development at Showtime as a drama series. Per the site, "Conquest" will be "a classic war story about two powerful men and their people ultimately leading to the destruction of the Aztec culture and the men themselves.”
Oscar-nominated playwright Jose Rivera (of "The Motorcycle Diaries" and "On the Road") will write the screenplay, and Brian Grazer will executive produce the project with Howard. Howard's been looking into making a film about this subject for years, though the sprawl of the story lead him to take it to Showtime.
Unrelated to Howard's project, but worth knowing: When "Deadliest Warrior" pit Ivan the Terrible against Cortés in an episode that ran last year, Cortés totally won.