One thing that bluesky did very well was abstracting the decentralisation (i know, its not really decentralised, bear with me) was having “apps” be centralised. What if we just pointed people towards a lemmy.app thing and that had a server as default?
Alexandrite.app does this, but it defaults to lemmy.world which is a bit of a dealbreaker.
Edit: By “app” I mean client.
Mastodon.social has a “spam problem” because they’re the largest target. We’re lucky it’s them because they’re one of the few instances with the resources to take on the problem. They’ve also contributed a ton - in tools and strategies - to help other instances deal with the problem.