I once had a vague idea to do a 1960s X-Men film poster (but it's way beyond my capability). The only part that I'd cast was Yul Brynner as Professor X.
I'd also envisioned a retro Transformers film poster. It would have featured Spike and Carly on the poster (I hadn't cast the parts) as well as a guy in an Optimus Prime costume (with an insert picture of John Wayne, declaring he's the voice).