This is a nonsensical way of thinking, but I couldn't help but make a rough estimate.
Assuming that, to be a recognized Mozart in the 18th century, you'd need to be male and live in Europe, that gives you a pool of about 60 million people.
Scaling that up to 8 billion, that means that if we were to keep the population constant, but promote equity and opportunity, we'd have a 133 Mozarts running around.