It’s unclear what Constantine 2’s story could be about, but the ending of the original movie does set up several arcs, like Angela (Rachel Weisz) pursuing a career in the paranormal, if Weisz were to return for the sequel. Constantine 2 could also go in a completely different direction, with Constantine and Midnite (Djimon Hounsou, A Quiet Place 2) pursuing other investigations. With ample comic material to draw from, the possibilities are pretty expansive.
As of now, there is no release date set for Constantine 2. The project is currently in its early development stages, meaning there won’t be significant news for a while. Goldsman still has to piece together the script, and the greater story details are presumably still being worked out by Lawrence and the team of producers. Coupled with this are Keanu Reeves’ and Francis Lawrence’s busy schedules. Lawrence is currently spending his time working on the Hunger Games prequel, The Ballad of Songbirds and Snakes, and is also attached to the Netflix adaptation of the game Bioshock. Reeves is attached to about four franchises at the moment, and since his career is in full swing, it’s highly unlikely that the Constantine sequel will be the only work lining his in-tray for a while. The sequel to the 2005 movie Constantine, Constantine 2, won’t receive a release date for a while.