3) Supergirl Meets Batman
Despite the Gotham reference, the Arrowverse show you would think Batman would be least likely to join would be Supergirl. Most identifiable for its bright, optimistic tone, the notoriously brooding hero would surely be an odd fit for the series. If Batman were to appear on Supergirl, however, it could offer a version of the hero that we haven’t seen for a while.
Just like Hoechlin’s Superman was drawn from the Christopher Reeve movies and the traditional image of the character rather than Henry Cavill’s modern take, Supergirl’s Batman could take him away from the increasingly dark figure of the films and return him to someone a bit more hopeful. Someone not afraid to wear a bit of blue instead of just all black (or occasionally very, very dark grey).
Calm down, we’re not suggesting that we go back to Batman dancing the Batusi or having nipples on his batsuit. It just might be nice to show a slightly different side to the character for a change. One of the beauties of Batman is that he can be interpreted in so many different ways and still be recognizably the same character. This seems to be something that has been forgotten in recent years and Supergirl could be the right place to bring that back.
Supergirl getting the coveted Batman cameo could also make sense, seeing as it already has Superman on board. What could be a more natural way of bringing Bats into the fold than by having Supes call in his old pal when he and Kara need his expertise.