Marc Guggenheim (who helped create and currently produces the CW slate of superhero shows with Greg Berlanti and Andrew Kreisberg) admitted that “there’s a lot of desire on everyone’s part” to bring John Constantine into the DC universe on the CW, and that “it would be wonderful and we certainly have a million ideas,” but he seems less optimistic about an Arrow/Constantine team-up than Amell and Ryan do.
In an interview with Variety, he said the following:
“It’s hard for me to say mainly because A: it’s not my decision to make and B: with Constantine being shopped around other networks… it’s really hard to make plans when a show’s kind of in limbo.”
It simply isn’t feasible right now to start planning big crossovers with a show that may no longer exist, no matter what your stars may want. It’s unlikely that Constantine will land at a place like the CW where interconnectivity would be easier, and network-wide politics may keep it from happening altogether if the show finds a new home.
Honestly, we’re more likely to see Oliver Queen and John Constantine interact with one another if Constantine doesn’t get picked up. The CW would then have the option to use the character as it saw fit, without having to worry about dealing with another network. That’s the less exciting answer, but something to think about nonetheless.
Until we know the fate of Constantine though, any and all crossover questions will remain unanswered.