Hát, ha vár szóbakerült a bttf.com, ott olvasható egy "inside source" szájából (és bocs a nyers importért):

We do not have the commitment of any previous actor in the BTTF trilogy yet. In fact, the current script does not call out for any previous actor (save one). It is entirely built around new characters in a new, entirely unique set of circumstances. The film is a fresh spin on the BTTF storyline, opening the door for a (hopefully) fun, new series of films. I, for one, feel that the McFly story has run its course — the technology lends itself perfectly to new stories.

The soonest you will see a BTTF film congeal would be 2003.