Actually, the Wachowski brothers (of Matrix film fame) had a script for a Plastic Man movie (they're big comic fans). They couldn't get a studio to buy into it though (this was before the super-hero movie boom) and they ended up making the Matrix films.
...not making this up...they actually wanted it to happen. The finale was a giant fight sequence where PM was fighting another guy who had turned to plastic in a factory that was (through some unexplained process) becoming pastic around them as well.
In any case, it could be wicked funny. I look forward to it if it actually happens.