Looks like Telltale Games has been reading my thoughts. Sneaky psychic game designers. I briefly toyed with the idea of a Back to the Future game sequel, one in which Marty is much older and Doc still lives in the Old West. Marty's kid takes a joyride in his DeLorean and completely screws things up for Marty in the present day. Somehow Biff becomes president, and the entire country falls apart. Marty marries someone other than Jennifer, thus preventing his kid's own existence. When his kid disappears, the DeLorean gets left in the past. Marty has to steal the time-traveling train from the Hill Valley museum, which has been there since 1885. Doc Brown covered up the time traveling mechanisms and donated it to the museum to preserve it, just in case.
I imagined that since Marty's kid screws up so many different things in the past, Marty would have just as many missions to set each thing back to normal and bring back his son. That's about all I came up with. I couldn't think of how to make fixing things fun, and I wasn't sure what kind of game it would be.
But it looks like Telltale Games, a group of ex LucasArts designers, is now making an episodic Back to the Future game. If it's anything like their creation Sam and Max: Season One, it will be great. I'm definitely interested to see what kind of storyline they come up with.
Read the press release here.