"EThe Bitcointalk Times 18/06/2024 Larry brings the forum into the chain". Here you go, that's the genesis message for if it is ever archived in the blockchain.

maybe bitcoin could have a sidechain that stored the forum. and people could get rewarded with bitcoin when they stored significant parts of it. like mining the forum.

instead of proof of work it would be proof of storing the forum.
I would say that having backups of the forum as torrents is going to be a easier solution and a long-term one. There are some torrent sites that always release the backup of their torrents library and such thing can be done with this forum as well. But doing something like that is going to be costly if it isn't supported by the community who may seed those torrents for the peers, and leechers.
But how big can torrents be allowed to be? Because this forum has to be terabytes in size by this point, after being online for over 13 years. I would guess terabytes but I really am not sure. But lets assume it is terabytes. I don't think too many people would seed something that big. Unless they were getting paid hence my sidechain idea above.
Lets say 100 new threads are posted to the forum everyday and each thread is 5 kilobytes. Then that is 500kb per day. that works out to about 182GB per year. Over 10 years, that's almost 2 TB. it is probably even more than that, in reality though...