Character appearances that never happened

In Shared universes or closely related films, especially sharing continuity with others sometimes plans fail when it comes to including characters. What are some characters that nearly got introduced into a film you loved but for some reason didn’t happen? How would their character have been shown according to the creative staff, and if you feel like speculating how would they interact with current characters?

I allways wanted to see the Vega Brothers prequel movie that Tarantino always talked about wanting to make. Madsen and Travolta are too old now so it'll never happen, but it probably would have been dope.