The forum itself doesn't belong on the blockchain, but the intriguing idea is the bundling of the BitShares client with access to this forum.
If our public keys were tied to our forum ID and access to the forum was only through the BTS client, the benefits described by the OP could be realized.
I proposed that idea months back. I think that is something they might have planned in the new interface.
I think it's a great idea, and it wouldn't take that much effort to accomplish. I also think MeTHoDx's idea of using a p2p address is excellent, which shows that BTS uses it's own inventions internally.
Even if all we did was remove this forum's DNS domain name and made it only accessible through the BTS client (thru a p2p registration) it would funnel more interest in the client, if nothing more than by the "hidden/special" but yet public access that would provide. People are curious and intrigued by mysteries.
Of course once p2p became popular and plugins / add ons or other tools are available to access p2p internet sites from their web browser the curtain would be drawn back so access would no longer be hidden. The use of BTS public keys as forum ID tokens could be done at any time.
If this idea were implemented the bitsharestalk.org URL could be redirected to a simple landing page that describes the BitShares ecosystem (including how to access the p2p forum) but "for more info" links to several other forums like Beyond Bitcoin and others.