This is the thing that I was thinking about. That a blockchain-like solution would better fit the goal of the extension. And I don't think this because I worry about censorship or free speech. I think the main benefit of this extension is that it creates an option to comment on sites where to creator of the site didn't make commenting possible.

However I do worry about moderation and trolls. Allowing people to make as much noise as they can is almost as damaging to free speech as censorship. I'm not really familiar with IPFS, what does it mean that unpopular comments disappear? Is it like seeding the only torrent (comments) that you like?