"There are no official producers on this project yet, but their interest has been tapped.  For the record, Mary Steenburgen said she's interested in reading the scripts; Christopher Lloyd said 'only if Bob Zemeckis is involved'; and Michael J. Fox hasn't been contacted at all, although he is mentioned twice in the treatments.  Any sign of interest is a good sign, especially once money discussions begin.  Writers for sequels are generally given a guideline and often get help from the higher-ups by placing phone calls to their reps and/or agents.  Nine times out of ten, a sequel will go ahead with the principals involved, yet with the option of writing them out.  Sequels are a lot harder to write than people think — they're heavily watched by the studio heads and can be exceptionally nerve-wracking on the writer.  That's why the majority of new screenwriters in Hollywood are hired to do sequels."

"In terms of BTTF4/5, Ed Solomon wanted to write about Doc Brown and Clara.  Solomon had no input from Universal and/or Amblin whatsoever.  In this case, if Lloyd opts not to join, BTTF4/5 is dead.  Simple as that — and we'll file it away as another 'project that almost was'."

Sources say next century to bring new ridefilm for 3 “Rides”