Personally I think it could be done. It could be about doc brown's child And Marty's son or daughter. Finding the old time machine car that Marty tried to put back together after it was hit by the train In an old garage. They have no idea it's a time machine as they think it's just a antique car. They put it in the year 2015 as they are playing with all the numbers and buttons. They can use some of the clips from the back to the Future 2 and AI to put Michael j Fox's face onto a look alike and asked Michael j Fox to voice over it for any needed scenes. You know when they're in 2015 they're going to mess something up that affects their future. And needing to travel back again to 2015 to fix it. They act like it's not a possibility but there are things you can think of. Do I think it's going to happen not really. But it's a possibility.