Do you think he would unlock Mangekyou? I think he would, it was a huge loss for him back then, and he got a base sharingan because of it. Would the storyline be any different?
No doubt about it, but he would have no chance of using it until he was at least 12, because his chakra reserves wouldn't be large enough, and even at 12, at best, he might only be able to use it once a day.
That would be so Op to unlock the ms at chunnin exams. No one would touch his power but more likely orochimaru would have orgasmed 2ice as hard and taken his body ASAP.