I'd not yet call it failed, but it's not yet succeeded either. To my mind, one impediment is something that lemmy.world shares with today's reddit: If you look at the front page it's 99% memes and images. That's the first impression people get, and it probably drives away a lot of people who might want anything else. We need those people to make more text-based communities come alive, if it's to evolve into anything like the old reddit.