The report actually mentions that Steven Spielberg is developing both at the same time, but that Indiana Jones will be first with Steven Spielberg likely to start filming in 2019 for a 2020 release date.
Regarding the West Side Story, it’s reported Steven Spielberg has begun casting on the project which will take some time as Spielberg is planning an extensive search to find the right actors.
Back in 2015 or so it was reported that Chris Pratt was eyed to be a part of Indiana Jones 5 along with Harrison Ford, but it is unclear if that is still happening.
Interestingly enough, Chris Pratt had some fun on social media with Guardians of the Galaxy director James Gunn with mention of snakes (Indiana Jones is known for being afraid of snakes). Maybe plans for filming on Indiana Jones 5 are interfering with the Guardians of the Galaxy 3 shoot?
@jamesgunn I noticed you haven’t answered me. Let me be more specific. Can the villain in volume 3 be a guy who has a cardboard box full of snakes, yes or no? If no. Then how bout just a handful of snakes and he says, what up wit snakes? And then throws the snakes at us?
— chris pratt (@prattprattpratt) January 14, 2018