I dont like Shazam, but ill see it because of Dwayne. I think he could kick ass as Black Adam. It's a character that people have associated with the Rock for the last 5 to 10 years, something like that. So it's cool that he'll finally bring it to life.
I predict that the Green Lantern movie will be Hal training John Stewart. Hal will either have a cameo at the end of JL or in Flash. Only brought into JL 2 as an important character.
Im not sure if Flash will be in B v S or not. Hard to tell. Ill take a guess and say the lineup for the first Justice League will be minimal (Bats, Supes, Wondy, Aquaman, Cyborg). Cyborg having the least amount of screen-time. Flash having a scene or two but only used as a build up for his solo film one year later. Once we see Barry Allen in his own solo movie, he'll crush it as one of the big members in Justice League 2.
I see JL #1 as a Trinity film featuring Cyborg and Aquaman helping them out from time to time, against Brainiac. 1 villain.
By the time we get to JL #2..we're looking at the full team of seven members. All up against Darkseid and his many minions. That will be the last team-up and probably the last superhero movie Snyder does for a lonnng time.
I see a Superman movie and a Batman movie happening before the 2nd Justice League. If that's true, i see Supes "dying" at the hands of Doomsday only to return halfway through Justice League in 2019 to take down the mighty Darkseid. In Batmans solo film, he will go at it with the middle-aged Joker like in DKReturns. Just like that graphic novel Joker will die & Bats will be injured quite a bit. Alfred and Dick will fear that he may die at the end but he'll pull through. So when JL Part 2 opens, we see Bruce Wayne inactive as Batman but in a Nick Fury leader-type role for the league. Supes will be presumed dead (only way this Superman movie doesnt happen with Doomsday beforehand is if Doomsday is the villain in Dawn of Justice). So the marketing will be about Bruce leading this team of heroes that include Barry, Hal, Arthur, Victor and Diana...and of course they will tease the returns of Batman and Superman to get everyones asses in the seats for the big finale. They'll have to cast HUGE for Darkseid as well.