Or has anything ever been said or done that'd make his existing in that world impossible?
The reason I ask is that early on it was suggested the new Supergirl show, running on CBS (which is half owner of the CW), could take place in the Arrow/Flash universe, allowing for crossovers.
More recently they've made it plain that Superman already exists in the world Supergirl lives in.
If any crossovers take place, he'd also have to already exist in the Arrow/Flash universe, unless the crossovers involve dimension-hopping.
From everything said and done on Arrow and The Flash so far, is it possible Superman already exists in that world?
Thanks to Superman board poster!