Okay, assuming this is anywhere near correct -- that's a full 32 months from the currently vacant May, 2021 unnamed MCU movie slot.
Stay with me here! LOL
20 months from now GotG3 is coming out (May, 2020)*
It's expected to be big, epic and expensive with tons of CGI (obviously)
What Guardians has right now is -- a director, a (recurring) cast and a first draft script.
The logic follows that if MCU could hire a director, get a first draft script and hire the main cast in the next 12 months -- Fantastic Four would be in exactly the same timeframe for a 2021 release as GotG3 is right now.
And nobody is saying the 20 months is not enough time to get GotG3 from where it is now to the screen in 20 months.
I assume there are some good directors (either MCU vets or new ones) who would jump at the chance to direct it. And I would assume there are script writers in exactly the same situation.
Alright...ready, set, rain on my parade.
* I am assuming that GotG3 is in the May, 2020 slot.