I think one thing the show has an opportunity to do, is highlight what a curve ball trial by combat could be. Tyrion could name Jaime his champion, with the knowledge that Cersei/Tywin wouldn't put him up against anyone who stood a chance of killing him. So then Jaime would either have to get Tyrion out of jail or be a total dick and refuse the request. Then how would it work with Cersei? Tywin would abhor the thought of both his male heirs being knocked out in one blow but is Cersei's lust for blood insatiable? She's grown distant from Jaime, but enough to send him to his death? Such a good delima that seems really in line with the show's exploration of the shades of gray of morality, and they never even explored that possibility in the books.