As of right now, just fantasy, but every once in a while you hear rumors that something might be in the works.

Coppola is pretty lukewarm about it. (That is, he has vacillated between saying 'maybe someday,' and 'no freakin way.') Puzo was very much in favor of it, before his death.

Some of the principal actors involved - DeNiro and Andy Garcia - have said they would be interested. Pacino and Shire have been noncommittal, although reportedly, Pacino recently seemed interested.

Of course, Coppolla does not own the franchise - Paramount does. Ultimately, it's up to them.