Nothing was stopping them from using Onyx (Female POC Samurai-Green Arrow ally) if they couldn't use Katana for whatever reason.

And I'd always thumbs down to DCEU movie where we get ANY Batgirl, Cassandra Cain included before we get a Batman movie.

DC big screen ideas are so godforsaken its funny.

Eternals might be Jack Kirby's least profitable idea (even it's biggest fans don't care all that much) and that is a way better proposition than
Birds of Prey the way DC has gone about it.