Fans know that Grant Gustin is heading to National City for a The Flash- Supergirl crossover in the 28 March episode, and since Arrow belongs to the same DC TV universe, there is a possibility of an Arrow-Supergirl crossover in the future.
Actor Stephen Amell, who plays Arrow, in an interview with IGN said he would "love to go over to Supergirl". When asked about the possibility, Amell said: "Sure! In this iteration of the DC Universe, the 'Television Universe' as it were, I'm the guy that's been around the longest, so I always feel — whether I'm on a show or I'm not on a show — I always feel as though I can in some way, shape or form represent them, and I always want them to be wildly successful and last for many more years than we end up lasting, because I just want to see people have success."
"So I would love to go over to Supergirl. That would be a blast, if for no other reason than I miss shooting in Los Angeles," he added.
Fans would like to see Oliver Queen and Kara Danvers fighting some Kryptonian adversary side-by side. Also, a three-way mash-up between Supergirl, The Flash and Arrow will be something to look forward to, maybe way long in the future.
Kara and Barry Allen will come together in Supergirl's episode 18 titled Worlds Finest. Actors Gustin (Barry) and Melissa Benoist (Kara) have already wrapped up filming for the special episode.