Well if there was any doubt, which I doubt there was any, Greg Berlanti himself the man behind many of these great shows (Arrow, Supergirl, The Flash and Riverdale) has given his confirmation.
— Greg Berlanti (@GBerlanti) February 27, 2015
As you notice he gives the hashtag #SuperheroTeamUp, is that possibly a working title? Marvel and DC both own the rights to the word Superhero, so it could be doubtful if Marvel gets royalties as well. You’ll also note he says he is more excited for the cast signing on, is this cast from the two established shows already? Could it be some from the CBS Supergirl series or the new characters? I have a feeling its the later for now. He also tells us more to come, so it looks like the series is further down the line than we might have been led to believe. I do hope to see it as either a mi season premiere or possibly a Summer series, back in January the CW president had discussed the possibility that we will see shows during the Summer time and a series like that would fit PERFECTLY, it allows all the shows actor to keep working without the commitment of having to hold themselves down as they would be recurring and it would allow more the occur in between seasons of the Fall shows. That does mean we’d have to wait until Summer 2017(depending on how far they are into it could be 2016) but it would be breaking the norm once again on DC’s part.