All of that sounds very rational. It's inspired a thought. What if, rather than rebuild a forum or start from scratch, you only work on the following things to create a "universal protocol module". Master that first, then be able to use it as your foundation to begin a forum later, with all the support you'd want.

Select an existing protocol, tweak it, fork it, and/or just design a new decentralization protocol as necessary.

Build just the decentralization module with adjustable settings to interface with existing forum platforms that would input/output from their databases, manage federated networking, and have maintenance tools and options. Also, build in room for many extra channels/settings to come in the future (ie. metatags and metadata).

Improve this "new protocol module" to be able to also deal with the half dozen other decentralization protocols. Also build extensions for this module allowing various existing forum platforms to plug in. This would not only make it the "universal adapter" but this would be the foot in the door to...

Become the best decentralization protocol module.

By providing equalizing tools you can directly set up federated forum fairness (rather than federated servers) to prolifically succeed.

IMO, decentralization is the most important part of everything we need to resist tyranny. That's why I think we'd need to fix that first.

Lemmy is what it is, but sharing the federation is a simpler GUI in Lotide (https://sr.ht/~vpzom/lotide/) which may be easier to start rebuilding from. I don't know if it's better or worse for your purposes.

Perhaps sharding databases (as with Ethereum, blockchains, torrents, etc) might help too.

I've only heard of these concepts to be able to mash and present them, so I don't know if any of this is obvious, impractical, or maybe even useful.