Guggenheim mentioned that his and Berlanti’s script for The Flash movie had Green Lantern show up at the end. He said: “We did a Flash screenplay and Hal Jordan showed up at the end of Flash.”
original plans for The Flash movie would’ve included Green Lantern showing up at the end of the film.
Considering that Berlanti and Guggenheim both co-wrote the original screenplay for Martin Campbell’s 2011 Green Lantern film, starring Ryan Reynolds as the eponymous superhero, it’s possible that the Hal Jordan that showed up at the end of their Flash movie would’ve been Reynolds’ Lantern.
The studio recently reworked The Flash solo film into a Flashpoint adaptation, potentially starring Ben Affleck’s Batman.