> I'm sure there's some blockchain based commenting thing out there...
Now that you name it, I totally forgot that Steem has a pretty good commenting system, and probably they're storing the entries on-chain. So maybe the answer is adding Graphene to the mix (Filecoin + Webtorrent + Graphene 2.0 as Blockchain-based distributed DB):
https://steemit.com/steem/@steemitblog/steem-developer-updat...