For Ra's Al Ghul , i'd actually go for an outside the box choice and characterization for the character. Instead of going for an older gentlemen with gray in his hair or someone who's more of a father figure , I would actually go for an actor much younger and around RP's age.
Ra's would have more of a youthful and angelic look akin to a young man in their mid to late twenties, even though he'd be hundreds of years old. It would further add to the Eeriness of the character when he stands next to Talia , who physically, looks around the same age.
He'd also come off much more as a young , ageless, dynamic leader of the League as opposed to the other versions we've seen.
For that version of Ra's, I'd cast Rami Malek.
