I appreciate your time and energy to think this idea. But decentralized isn't needed/suitable for use case you mentioned. And based your explanation, it's not decentralized. You might want to check IRC and Usenet as example of decentralized/distributed forum.
Some of which are, to make the forum hard to take down, to have post of members preserved even if the forum database is destroyed/corrupted from a single point etc. Incase of the latter, the forum copies can replicate and continue to exist possibly with another domain name (if necessary). The right domain name which should be accepted as the real forum domain name could be choosen via consensus involving most/all forum participants
1.
https://loyce.club/ and
https://ninjastic.space/ partially solve problem of preserving forum database.
2. Moving to different domain (and optionally different server provider) isn't decentralization.
So, I'm suggesting the development of a forum that works offline with members forum data saved in their devices, more like how Telegram or similar messagers do it.
Most messengers is centralized. If you just want ability to read post offline and other certain action (posting post, sending merit, etc.), it can be solved by creating an application which can download part of forum and automatically perform certain action when it has internet connection.
Higher ranks will automatically get higher moderators access. And moderators should be ranked based on merit.
This will lead to disaster.