Mastodon's problem is going to be the same as Lemmy's. I tried to switch after the Reddit APIcalypse, but needing to choose a homeserver and finding out they don't see content from wherever <reddit community> migrated to because of your homeserver's politics or whatever, kills it for most users.
It's great for people who care about users and communities being able to self-moderate, but Joe Average couldn't care less if it happened on Venus in an alternate universe. They just want to sign up somewhere and be able to post and see others' posts.