I wouldn't mind seeing some take on the "Death and Return" story for the third film. The trick IMO would be to do it without it feeling like a straight-up rehash of "The Dark Knight Rises", which basically went down a somewhat-similar path. Maybe have Superman lose his powers in some kind of sacrifice play at the end of the second film as some alien menace to make Zod's army look like Romper Room is seen advancing toward Earth, and have him spend the bulk of the third film looking for a way to get his powers back while said menace is running roughshod all over the Earth. It's not QUITE death, but what the heck, the rest of the world would think he's dead.