I heard that ??? (Also known as the blue baby) is Isaac. I know it's not probable,but hey,some say that isaac comitted suicide,but where? That's what i'm going to answer: ??? is isaac's corpse. The chest has time paradoxes.remember ending 6 where mom's arm grabbed isaac? that was an paradox. When isaac finds ??? it's himself,the story behind this is:
After the in-game events,isaac comitted suicide in the chest in his beedroom after reading the story in the Bible,the pictures of his family led him to his suicide due to the one his mom with an knife.
The end music is isaac singing a hymn while suffocating in the chest.
So... ??? is Isaac?