There are a lot of good points here, I appreciate the time you put into it.

As an end user of both Lemmy and Mastodon, it's always an eye opener to see how developers greet user requests and suggestions with curt or snarky replies. Even "Why don't you open an issue on our source tracker" will often effectively shut down suggestions from less tech savvy newcomers.

My own concerns are more on my own level, though. It resonates with me when you write —

The Fediverse has its own existing cultures that thrive here. And when you enter a space that already exists you need to be mindful of that to prevent issues from occurring.

I've seen a few user migration waves, and I think your description of (some) Lemmy users who just want a drop-in Reddit replacement is on point. Mastodon has had its share of Twitterati who surged in trying to recreate their previous circles and tone. Obviously, it's a generalisation but we do need to face the problem.

The transition from a walled garden environment like Reddit or Twitter — moderated by professionals or enthusiasts, and algorithmically curated — to a federated space with carefully cultivated etiquettes will never be like simply picking up a conversation in another UI.

I'd be interested how a project like Sublinks would/could accommodate the existing fediverse cultures, and hopefully bridge the cognitive gap that seems to exist between threadiverse and fediverse?