Confucianism isn't much of a missionary religion, one could say it spread in the same way Roman culture did throughout its empire and its environs- because other societies saw that it was great, and decided to pick up on it. But could Confucianism have spread further in the world?
And no, 17th century Enlightenment Europeans being interested in it doesn't count. I'm talking about more Confucian states, maybe even the institutionalizing of Confucianism as a deistic civic religion. (Though that wasn't even much of a thing in China, I think. I don't suppose people went to temples of Confucius regularly like Abrahamics would go to church of mosque or synagogue. They'd more likely pray at folk shrines.)