Originally Posted by LordKinbote
It would be neat if HE duplicated as well.
Well. There is the 'Double Visions' episode.
At first I thought it would mean Marty coming back to June 13th 1931 AGAIN (meaning he will see two other Martys doing their bussinesses), but considering it's during the Expo - this is out of the question.
The other possible explanation I can think of is having both Doctor Brown and First Citizen Brown as characters who would work together (the reason behind this is that in 1985A there did exist two Docs and two Martys with different fates, so it's possible).
And, well, maybe Doctor Brown DID duplicate. Maybe a Doctor Brown was erased because of the First Citizen Brown, but the other's still alive and kicking! Though one would ask why didn't the second Doctor Brown who went to the future didn't fix the Time Machine. And abandoned it to hell also. And never came back for Marty or thought about him... Um... Hm.