So the first thing to note, there's not really any moderation done for the join-lemmy instance list. Any instance that has a description and icon will be listed on that page.

Now imagine the scenario where a pro-fascist instance pops up. As a new user, you may be pushed to join that instance. And as a new user, who has had the fediverse abstracted from them, you're on that instance, the instance has been defederated from all of the decent instances, so you look around and all you see are racists, homophobes, and Nazis. A user subjected to that experience would walk away and say to themselves, "wow, Lemmy is a cesspool".

I don't mean to shut down your idea. Maybe there is a way to abstract the fediverse and still result in a reliably good user experience, or maybe rather than abstract it there's a way to educate users better. Or maybe a little of both.