Green Lantern Corps was one of the first movies to be announced for the DCEU, and if Warner Bros is at all interested in taking audiences on a ride to across the DC cosmos, this movie is the best way to do it.
In the latter movie, several Green Lanterns were shown in the flashback battle, but there was no explanation provided about them.
So far in the DCEU, our only exploration of the DC cosmic mythology has been visiting Krypton in Man of Steel and Justice League having Steppenwolf and his Parademon army invade Earth.
Now that Geoff Johns, the man who redefined the Green Lantern mythology in the comics for nearly a decade, has taken over scripting duties on Green Lantern Corps from David Goyer and Justin Rhodes, hopefully that means the project will happen sooner rather than later, though there’s no way it will be ready to go by 2020 as was originally planned.