I don't really want to make a big fuss about it but couldn't number 7 refer to "completing" maze 6? Like, he doesn't specifically say he "finished" maze 7, and in the tweet he only talks about starting research on maze 6...
Now, granted, it's possible that he's just being coy, and maybe he even just wrote a ton of different scripts because there hasn't really been a clean slate locked down until now (that mystery pitch is still scratching in my brain), so he kept writing outlines just in case, and he does have 7 scripts written. But it's still interesting to think about an event with only 6 mazes and a gauntlet, kinda like in 2016.