Lemmy has a lot of obstacles that will prevent it from truly going mainstream:

1. The community browser is complete dog shit for discovering content on different instances, and trying to view another instance's content from your own community is just needlessly complex. Discoverability is still a lot better than Mastodon though, where you'd look at all post and see nothing but hentai reposting bots regurgitating stuff that isn't even allowed on NSFWLemmy...

2. Due to the nature of federation, you also run the risk of committing to an instance only for them to defederate entirely, or disassociate from content you want to see but they don't agree with. Beehaw is a very good example of this.

3. As there's no option (yet) to migrate to a different instance, and Lemmy is a FOSS project that cannot be monetized in the same way as a traditional social media site, what happens when instances start shutting down due to being unable to keep up with server hosting costs?

4. I cannot speak for the iOS option available, but Jerboa is barebones. For example, you can't even tap on a post/comment reply in your inbox to go to that comment's permalink and view the context. This is incredibly basic functionality for any social news aggregator. Even with the fediverse in general surpassing 150,000 users, I don't see Lemmy getting the same level of third-party app support as Reddit had.