Honestly, I don't think a centralised app is really a good solution in this space. It's going to be big, it's going to be expensive, and as soon as someone tries to pay for it, they're going to end up repeating all the same mistakes.
I actually think a large problem with lemmy is that it's already too centralised. Each instance is trying to be a reddit. Which is all very nice, but it also means each instance is effectively in competition. I think each instance should be trying to be a subreddit.
The way it'd work in my head is that you'd have two types of instance. Front-end instances that are effectively curators/aggregators & identity providers. They effectively get to present you your front page and r/all. And this is entirely "if you don't like their curation choices, pick another". So here you'd get to pick if your instance is tech-focussed, foss-focussed, as-big-as-possible, family-friendly, politically charged, etc.
And honestly, the only thing stopping that instance from being an app that's not much more than an rss feed-reader, is that I've saddled them with being identity providers too. Which is not the world's biggest hurdle.
The second type of instance would be one subreddit. So moderators are instance administrators, you're trying to build one community in one place, etc. You're just trying to build one community in your one niche/topic, - and you're not trying to compete with other instances who are also trying to be everything to everyone.
I think this would present a lot of benefits. Front-end instances would naturally discover subreddits through the subscriptions their members make. For users, discovery would be through cross-posts, and curation amongst the subreddits their home instance already knows, etc. They can choose their own funding model, ad model, membership model, etc. And if they make choices that are wildly unpopular with their members, they can move to an instance with different ideas/ownership/spez without losing their communities in the process.
For subreddits, administrators can control their costs by, eg, choosing only to host text posts instead of images & media. Brand-owners can own their own communities/identities - ubuntu can run r/ubuntu on their own infrastructure with their own moderators, etc. And we should see a lot less pissing patches like the linked post, because subreddits aren't directly leaning on each other. Hell, there'd be nothing stopping youtube exposing their channels as pseudo-instances.
What I'd really love to see is a return to a world where one person can host their niche community on a $5 VPS - and still get all the benefits of being a subreddit. And at the same time, foss communities & company support forums can join right in without it being a huge risk to themselves, etc.
Asking for centralization is asking for another model where we put all our eggs in one basket, and then wonder why that basket has to kowtow to VC to pay for it all. What worries me is that right now, we're very focussed on breaking free from that, and no-one's exploring what we could actually gain from the alternatives.
And while this risks sounding incredibly hand-wavy - it's really just the forums we all grew up on, sharing a common API.