I would bet money on we will eventually see Doomsday make his appearance in the films. What I would like to see happen is parallel what they did leading up to "The Death of Superman". For an entire year DC ended almost every book showing a mysterious fist pounding on a wall, that was eventually reveled to be Doomsday breaking out of his cage leading to one of the most epic battles in comic history.
I hope DC does almost the same thing in the film series. I think each of the upcoming DC films should have a post credit scene simply showing Doomsday pounding on his cage. I think this could span a year or two, and possibly have a few scenes that show the world recording seismic activity to drop a few hints here and there. Before finally having Doomsday break free for a JLA film or a future MoS film leading to the epic battle and death/rebirth of Superman.
What do you think? Would this work in the movies as well as it did in comics to build up to this amazing fight? And would you want to see it happen?