^It's not like they need to get a big name in the role to put bums on seats though, is it? Michael Shannon isn't a box-office draw, nor is Kevin Costner the big name he once was. Zane only really had two big hits in his career, Dead Calm and (obviously) Titanic and in neither of those was he the major attraction.
Not that I think he'll play LL in MOS2 but I think they'll cast who they want in the role, regardless of that actor's box-office friendliness.
I hear what you are saying that Superman is relatively star proof--as in they don't need a star to sell it. But, I could see them using a "big name" for the role of Luthor. Be it someone with real acting chops, like Shannon, or a big name. I think it would be to good of a PR thing for Warner's to pass up.
Like Brando as Jor El. Or Crowe as Jor El.
It could go either way.
That said, the box office success will give the team enough cred to make WB's give them freedom of casting.