The way the site's content is stored can be a problem. But the even bigger problem is making the site functional for anyone. All information must be accessible within seconds, for anyone who enters the site. No need for downloads or other extra programs to access.
I believe the OP meant the "decentralized storage" as a backup solution, not as an actual proposal to move Bitcointalk entirely to a decentralized platform.
But even if this was the case, there were already models for on-chain stored "forums" or "social media" that worked. I had discussed that here on the Meta subforum in
this thread. In my case I have had a bit of experiences with Steem(it), and it worked reasonably well. Of course it has centralism problems but these are not directly related to the fact that it's stored on a blockchain.
In the case Bitcointalk is moved to a Steemit-like platform completely, viewing content and also posting could be provided by independent websites which access the blockchain with a full node. The software needed is a combination of a block explorer (to view the content) and an online wallet (to post yourself). Every forum user would need to create at least one account/address/key pair for the blockchain to post, but that can be hidden (so in fact all what you have to do is to "register" on one of the "node websites").
In reality, this concept would be more on-topic here than it was in the other tread I linked above, so I guess the concept could be elaborated deeper here in this thread.