It may or may not take off to the point of replacing reddit, but I think the exodus if people now and especially after the end of the month will lead to it having at least the same amount of users as Mastodon. Maybe more, since the average reddit user is probably more tech-savvy and more willing to migrate to a different platform than the average Twitter user (since they follow subreddits rather than individual users). And a roughly Mastodon sized lemmy is more than usable to replace reddit imo