Sure, it’s possible. But for it to be effective, each member would have to have the entire SDMB database on his harddrive, and of course the P2P software to drive the whole thing. Of course decentralization causes a whole new set of problems for the moderators. Imagine trying to lock a topic…on 30,000 computers! It’s a nice idea, but impractical, I think.
Well, they wouldn’t have to rewrite the whole database with each post, just add the new post (if the software was properly written).
Also, you wouldn’t need a copy of the whole databse on every computer. One of the advantages of P2P is that you can have pieces spread out over different machines.
The biggest problem I would see from a P2P message board would be how to handle distribution of new posts.