After the Supergirl/The Flash crossover was a huge hit, fans haven't slowed down on requests for a crossover. If anything, since seeing how much fun it was to have Kara and Barry together, fans are just hungrier for more.
Well, it might not take interdimensional travel to make it happen next time, executive producer Andy Kreisberg teased in EW's "Spoiler Room" column. The Flash ep teased that if Kara Danvers exists on one Earth, that does mean she could exist on any other, including the "Earth 1" of The Flash. He pointed out that she would have to be a Kryptonian refugee no matter what, though.
"Any Kara that exists on Earth 1 would also have to have been an alien. It can't just be Kara Danvers from Poughkeepsie," Kreisberg said. If she becomes a hero on that world, though, she might have a "different costume," whether she goes by Supergirl still, or another Kara Zor-El identity, Power Girl, as EW posited.