7) Mrs. Doubtfire 2
A follow-up to the 1993 Robin Williams vehicle Mrs. Doubtfire was stuck in development hell for a long time – with Williams himself refusing to return, as he thought all three script treatments for the movie were terrible.
Eventually, director Chris Columbus talked him into it and the sequel was properly announced in April 2014. Sadly, just when things were finally heating up on the project, all plans were permanently shelved due to Robin Williams’ tragic death later that year.
Mrs. Doubtfire was never a film that was exactly crying out for a sequel, and the proposed plot about Williams’ character following his daughter to college doesn’t sound amazing, but the reason it was cancelled is just so heartbreaking. We would happily take a mediocre Mrs. Doubtfire sequel if it meant we had one more film to showcase Williams’ endless comic talent.