It has already replaced reddit for a lot of people. It would be difficult to surpass it, but after all it doesn’t matter how many users a social media has if most of them are lurkers. From what I’ve seen on Lemmy, people are more willing to engage with others. I’m one of those people, in the two years I was on reddit I didn’t make a single comment or post. Maybe it’s because the fediverse is much smaller than reddit and feels more like a community. In that case I wouldn’t hurry to “replace” reddit.