To make the movie Transformers accurately, yes, not only would die-cast be great, but a very large 20" Transformer might be necessary for each toy (larger yet for the bigger characters).
That being said, maybe Master Replicas or Takara-proper could handle these robots and sell them direct or through their distributors and just pay off Hasbro since they'd cost like $100+ each and wouldn't do for Hasbro's mass-market retail approach. (Target or Wal-Mart would probably not carry a $100 B-character like Ironhide, while Starscream might cost $200 if seriously done right and made to work as seen in the movie. Heck BumbleBee looks really complicated! And if I dare call Ironhide a "b-character," Blackout or whatever the chopper will finally be called is a "D-character.") I'd love to see them (and would pay for them) being done Masterpiece Quality or better. But I don't have my hopes up.