I've introduced two of my friends (not into tech) to Lemmy. Since they're not into tech this is their first web forum.
I've explained the federation thru the usual email metaphore and that's ok, but to lookup for communities is not quite there on client side.
Let me explain.
He wanted to see all the communities on an instance because that instance is in his native language but he's registered on another instance. So to see all those communities you must go on instance.domain/communities, copy the name of the community you are interessed in and paste it inside the app/web client to look it up.
And to see all the communities all over the fediverse you must use lemmyverse.net which is a cool site, but still you got to copy paste back and forth to the app.
This could be implementend inside app itself by listing all communities and add ability to filter by things like instance.
Obviously open to discussion about the issue itself and how that could be improved.
Feel free to tag apps/clients devs to ear their opinion too.
But how will you get a "universal" view of the fediverse? No single authoritative view exists.
You yourself acknowledge that this is complicated, but I honestly don't understand what appeal a hacked together fake centralized system would have for people if they don't care about decentralization in the first place. Any such solution is almost inevitably gonna end up being janky and hacked together just to present a façade of worse Reddit.
Lemmy's strength is its decentralization and federation. It's not a problem to be solved, it's a feature that's attractive in its own right. It doesn't need mass appeal, it's a niche project and probably always will be. I don't think papering over the fundamental design of the software will make it meaningfully more attractive to the non-technically minded.