Maybe to improve a scene or make the ending more epic or something else

Superman IV: The Quest for Peace. Considering half it's budget was scrapped (So Canon could also make Masters of The Universe) and almost 5-8 million of it's 17 million budget ended up on the cutting room floor, I would have liked to have seen the original concept realized with Bizarro and Reeve playing both roles. Also would have immensely helped flesh out all of the effects, and not have to cut so many corners.

I also think it would be an interesting experiment if Tarantino remade Reservoir Dogs at some point. Kind of like Evil Dead II or Desperado treatment.