I remember Billy Dee doing talk shows in 89 saying: "I took the part because something is going to happen to my character down the line... but I can't talk about it right now." He knew all about Two Face from the start. I knew what he was hinting at because I knew all about Two Face and was excited to see Lando Calrissian in the part.
As for Michael Keaton and Batman Forever
... from what I remember Michael Keaton decided not to do Forever
pretty late in the game. I think they made Robin Williams an offer to play the Riddler but he turned them down. No idea why.
Personally I thought Kilmer was a cool choice. Just look at his build in that movie. He was friggin' built! He did a lot of the fight scenes himself! There was no close up of Kilmer and then a quick cut away to a long shot so the stunt man could do the fight. Kilmer was kicking, punching, running, jumping in a 300 pound rubber suit!
I don't care if you like BF or not but Kilmer was fucking impressive! Didn't care much for his Bruce Wayne though.