I found this thread:
Of an hiphotetical Tim Burton Batman III and found this:
Trivia for Batman Returns (1992)
The character of Max Shreck was a re-write of District Attorney Harvey Dent; accordingly, most of his plot points would have perhaps made more sense if Shreck were D.A. instead of a corrupt businessman. The explosion at the end of the film was a means to injure Dent and produce the scars that would lead to his transformation into Two-Face for the third movie in the series. Reportedly, Billy Dee Williams took the role of Harvey Dent in the first Batman (1989) movie because he knew that the character would eventually become Two-Face. Williams' contract to appear in the sequel is rumored to have been bought out by Warner Bros. at a heavy price.
Trivia for Batman Forever (1995)
Before deciding not to don the cape and cowl for a third time, Michael Keaton met with Joel Schumacher and declined to join the project after deciding that he did not like the direction in which Schumacher was looking to take the franchise. In the brief time that TimBurton was still considering doing a third Batman film, Riddler was the only villain that he planned on using. The idea of using Two-Face did not come up until Schumacher joined the project.
While Tim Burton was still slated to direct the film, Robin Williams was running to play The Riddler, but after Burton dropped out, Williams lost interest and turned down the role despite being offered.
I think you could be interested in knowing the other casting choices and original ideas he had for the movie, aparently the Riddler wasn't going to be portrayed by Johny Depp and i think he would make the character more serious and less comical than he was in Batman Forever.
By the way, Tim said that he didn't like Schumakers batman titles so he didn't like names like Forever and Triumphant