Funny you should mention this but they are actually working together on a film. It's a sequel to an earlier film of his and will be called Hannah Takes a Contract Out on Her Sisters
Since De Niro has found a new niche, i.e. comedy, I would love to see him collaborate with Woody Allen. I'm Sure De Niro would take scale to make such a movie. I'm not sure if it was scale, but he took signifcantly less than his usual paycheck when he was cast in Cop Land.
De Niro was originally going to play the role of the clown in "Shadows and Fog" but there was a sheduling problem and John Malkovich ended up replacing him.