Ohh, then I stand corrected. I'm not intrigued. It's certainly looking as thought it's another Earth-38 show. Can't quite imagine what's going to bring Ollie & Barry to Earth-38 though...
Well, for all we know 'Clark's friend' may have been Batwoman all along. Everyone (myself included) took the implication that the mask-wearer and batears was Batman, but what if it was Batwoman all along?
The Arrow show has specifically mentioned Gotham and Bruce Wayne. The Supergirl show (to my knowledge) has only mentioned Gotham and Vigilantes (with bat ears); no mention of Bruce Wayne. I therefore wonder whether Batman doesn't exist on Earth-38.
I expect we'll have Cisco because he can breach about, but I'm not seeing too much use for Felicity, Ralph, Iris, Diggle etc outside of their specific shows, and even then, I'm expecting small parts.
It certainly seems like they're dialling back on the excessive nature of the previous crossovers and scaling back on the characters (which they really needed to do in my opinion).