This *is* that movie.
The Movie Critic, which was apparently going to heavily feature the character of Cliff Booth, has now been retitled The Continuing Adventures of Cliff Booth.
Basically, forever whatever reason, Tarantino decided that he didn't want The Movie Critic to be his tenth and final film, so he shelved it. Pitt thought the script was so good, though, that he asked Tarantino if he could take it to Fincher to possibly direct. Tarantino gave Pitt his blessing, Fincher too ended up loving it, and now here we are.
That said, how much of the script has been reworked - if it all - under Fincher is currently unknown. It could be the exact same script, except with a new title, or it could be that Tarantino or a Tarantino-approved mystery writer re-worked it to whatever degree. It's all very hush-hush and no one knows for sure yet.