While the future of the X-Men franchise on the big screen is something we know little about, the transition of the film rights back to Marvel has meant that the Fox franchise that has been going sine 2000 is at an end, or will be once New Mutants finally comes out. This means that, despite the popularity of the idea among fans, the on again, off again Gambit movie project starring Channing Tatum won't be happening, at least not as it was initially planned. This is unfortunate for a number of reasons, but one of them is the fact that the movie was apparently supposed to tie up a lose end from an X-Men movie from four years ago.
Simon Kinberg, who wrote 2016's X-Men: Apocalypse, revealed to IGN during a watch party event of X-Men: Days of Future Past, that the post-credits tease at the end of X-Men: Apocalypse which referenced the Essex Corp, and by association, popular villain Mister Sinister, was supposed to see its resolution in the Gambit film. According to Kinberg...
We had a tease of it at the end of Apocalypse. The Essex Corp is something that you see in a tag at the end of Apocalypse. We had talked about doing something with him, and I won't get into the specifics of it since it's no longer a 20th Century Fox property and now it's part of the MCU. I have no idea what the plan is. But Mister Sinister was going to be part of the Gambit movie starring Channing Tatum.
This is the first that we've heard that the plan for the Apocalypse tease was actually meant to tie into Gambit. When we first saw it, the assumption was that we would see Mister Sinister in the next proper X-Men movie, or perhaps he'd appear in the then upcoming Logan considering that Essex Corp. had shown up at the facility where Weapon X had been held.
Unfortunately, it seems that the plan to make Mister Sinister part of Gambit was a bit of wishful thinking, as the film never really got off the ground. The movie was something of a labor of love for Channing Tatum akin to the way Ryan Reynolds worked so hard to make Deadpool happen. However, while the movie had a star and a popular character, it couldn't seem to hold on to a director. A number of great names passed through the project, but never stayed long. The film was first announced in 2014, but its release date would get perpetually pushed back until eventually it was taken off the Fox schedule entirely.
It's still technically possible that a Gambit movie could happen under Disney. It's possible that Disney and Channing Tatum could still remain attached. However, what is a virtual certainty is that even if all that happens, the film will be entirely separate from the previously existing Fox X-Men films and will instead be a new part of the Marvel Cinematic Universe.