Utterances is a lightweight commenting platform built on GitHub issues. So you have to have a GitHub account, but I expect most people who comment on this blog already have one.
When I switched to blogdown, I lost my disqus comments. I had considered migrating them over, but never got around to it. I also thought that there had to be a way to link GitHub issues to blog posts, but didn’t investigate it much.
I’m not expecting a lot of heavy commenting, but at least it’s now available!