It heavily hints at Ra´s Al Ghul. He wouldnt be the obvious next villain like Darkseid or Braniac.
With the lazarus pit in play you could also explain dead characters coming back.
Nah, mate.
It's not Ra's.
For one, Ra's Al Ghul doesn't traditionally have an American accent. He's from the Middle East.
Secondly, I'm pretty sure Bryan Cranston was referring to the literal fighting pit as seen in the trailer. The whole speech he delivers is about the sense of re-invigoration that comes with fighting your enemies, hence the tagline featured in the marketing. It's purely symbolic.
I'm absurdly confident they didn't hire Bryan Cranston to play Ra's Al Ghul of all DC characters in this game. His inclusion certainly wouldn't fit the story they're trying to tell either.