I could see that. Who ever they put in there should be one of his main rivals though.
On a side note, the greatest superhero movie ever would be a Marvel vs DC like they did some years ago in the comics. It would be great to see the chaos and blood bath resulting from arguments over who would win in a fight, the Hulk or Superman or Spidy vs Bats. Fanboys everywhere would lose their minds. I believe a dimensional hole would open up and swallow us all.