This reads like somebody had a checklist of things that would piss off the fans.
I could see Eddie Murphy in a Batman movie but not as a member of the traditional set of villains. A better use of his talents would be as a regular person, perhaps a police detective, having to deal with a world that contains Batman and his bizarre opponents. Eddie Murphy playing crazy? Not so good. Eddie Murphy dealing with crazy people? Now you've got something.
Robin can be made to work if they emphasize him as Batman's link to sanity. But not played by a 20-something adult actor. That simply makes no sense. 'Batman and Robin' was the Village People of superhero movies, with a flamingly gay director targeting a very select audience.
The original screenplay for the Tim Burton Batman had a pretty setup for introducing Robin in a sequel. Dick Grayson's parents are killed by the Joker during a chase sequence that plows through the circus. This places Dick Grayson in Bruce Wayne's care by the end of the movie but leaves the issue of Robin for later films. This got thrown out when the casting of Jack Nicholson required a radical rewrite to accommodate the senior citizen Joker. The original intent was drawn heavily from Alan Moore's 'The Killing Joke' with Batman and the Joker being the same age and having a lot of similar history, with both of their lives sent into weirdness by having one really bad day.
I think Jason Alexander could be a good ventriloquist. An utter nebbish who expresses a violent dominant persona through his dummy.
My longtime pick for the Riddler seems to have evaded all of Hollywood. Jeff Goldblum. Recall him in the era of 'The Fly' and 'Earth Girls Are Easy.' Tall and thin but not wimpy. Imagine Seth Brundle saying, "Riddle me this, Batman" Some of his character dialogue in 'Jurassic Park' also offer some good example of how he'd perform the Riddler.
But that bird is flown and he's too long in the tooth for that role.
