Superman was a desperate move because you can't have Supergirl without direct Superman references.
S1 did it so terribly and with changing networks it was basically a marketing stunt.
Arrow doesn't need Batman so WB wouldn't approve of it.
However I still think
1. Supergirl will eventually use Batwoman
2. Teen Titans will use Batman in some form
Just have Batman exist in the past and be a LOT character: