While the recent “Invasion” crossover delivered an unprecedented DC crossover between Arrow, The Flash, DC’s Legends of Tomorrow and Supergirl, the Supergirl episode ended up only featuring a connection in the final moments.
“Because we weren’t aware that we were going to switch ‘Supergirl’ from CBS to CW and it was really going to be part of it — that was the one show that didn’t have built-in shut-down days, so all the other ones did,” Kreisberg tells the outlet. “Melissa [Benoist] ended up being heavily in Flash and then in Arrow, so Supergirl was the one we needed to shut down the most and it was the one that we didn’t have any opportunity to. Now that we’ve gotten the early pickup and we’ve started designing the seasons, we’re building in those dark days, and actually more dark days on Supergirl than the other shows, to make it a little easier… Next year, we’re hoping to do a true four-way crossover.”
Read more at http://www.superherohype.com/news/391609-cw-dc-crossover-event#cU7CXJlYf1YCBcqv.99