Well, regarding Mel, it was bad timing, when he was signed up and we were all ready to go, and then the Iraq war killed the US dollar and the funding fell apart. When things got going again, Mel's implosion had happened and he moved on. George Miller has said that Heath Ledger was slated to pick up the role, but sadly, we know what happened after the Batman movie.
I met Mel a few times in Sydney while working on developing the movie. I had some interesting chats with him about The Prisoner remake he was going to do in the 90s, which of course, never happened.
And also that he had the rights to Johnny Nemo (by Brett Ewins and Pete Milligan) and was intending to play the futuristic detective. ('Lock, Stock and 2 Flaming Bladerunners'). Now that, I would have loved to see!