Lemmy is basically guaranteed to fail the exact same way reddit did. More and more users flock to a few centralized instances (some of which are already starting to show very biased and manipulative administration...) which increases hosting costs and so forth. This leads to a need/desire to monetize and, no matter what people pretend, donations are not a viable path.

Which leads to shittier monetization approaches. Which get exacerbated by people being willing to pay a monthly subscription to the app creators to load the content, but not the sites that actually host it.

Peertube, at best, will be the phpbb to the vbulletins of the world, for subscription based websites for influencers. Sort of like how mastodon is the core of a few of the right wing shitholes. Not sure what the "educational" gun nuts are doing on their site, but I am sure it is only a matter of time until Ludwig or Toast try a premium site for their side hustles. They won't federate and they'll be behind paywalls but they'll save a lot on licensing. And, more likely, peertube will go down in a mess of CSAM and gorn.

Mastodon I actually see surviving. In a good-ish world, we'll see it being part of a decentralized social media that is resistant to corporate interests. News media and Brands will have their own instances that federate in to protect them from a deranged child of apartheid spamming swastikas everywhere. Is it facebook's twitter that is also compatible with mastodon? And I can see a world where a couple dozen major "instances" carry on. And this also actually provides a venue (and honeypot...) for social activism and sexwork.

But... most likely mastodon will become like usenet. It exists, a few people love it, but mostly it is just something your ISP might forget they are offering.