They moved to this away from the per-article comment system they used to have for news posts, etc. In the past anyone (no account needed) could post a comment on the documents they posted and have it displayed in-line with other comments at the bottom.

But then The Tor Project chose to move to a registration only forum where all the discussion of news is hidden away from the article. It's really impeded discussion of the tor project's decisions... which I think they consider a benefit. They didn't like having criticism of things like their early removal of tor v2 support on their main pages. Much better to hide in registration only forums requiring the latest bleeding edge browsers and JS to use, in part of the site no one visits.

Interesting issue with the U2F account lockout potential - due to the anti-phishing protection and the domain name changing I assume?

I thought this article would be about them hosting their discussion forum on a .ONION address.