One would imagine if an intra-DC Universe crossover was not discussed, a DC Universe and Arrow-verse crossover wasn’t either.
As cool as that may be, there are reasons to doubt that Constantine’s line in the Legends of Tomorrow trailer meant a crossover is happening.
This information makes Constantine’s line feel less substantial, and more akin to Cisco Ramon’s Marvel references on The Flash, than an actual clue the shows will collide any time soon.
Gary Dauberman, who wrote the Swamp Thing pilot and is serving as executive producer, said earlier this year that a Titans crossover with his show had not been discussed, and that the dramas will not connect right away.