There's the federated platforms, of course. Gab is a mastodon fork. Their monetization is via premium accounts. Spinster's-- this is an instance dedicated to women who don't think males can become women-- monetization is via community support. There's definitely methods here, just takes some creativity. The issues here lay in the fact that the fediverse is just as interested in deplatforming as the main tech bros. Fdroid won't host the spinster app on their repo, and tusky, a multipurpose mastodon mobile app-- won't let you log into either a gab account OR a spinster one.

Despite these issues, I definitely think mastodon, mastodon forks, pleroma, or other fediverse software would do just fine for Parler's userbase. The fediverse skews very liberal, and while there are a few pleroma instances dedicated to free speech, very few big instances federate with them.