This is obviously inspired by the recent Replacing Disqus with GitHub Comments post on HN.
I wanted to share something similar I've done with my blog. You're looking at it now. It's not using Disqus or any heavyweight 3rd party solution for comments.
Instead, I've created something very simple, similar to GitHub Issues frontend UI and backend, and used that. The backend is completely pluggable (it's an interface), so it can be implemented by talking to real GitHub API, or any custom implementation you want. My blog uses a simple JSON files implementation, so I can avoid a heavyweight database dependency.
When I first created it, I was using yet another
issues.Service implementation that was exposing my original WordPress blog (via its export as XML functionality). But eventually I migrated that into the current filesystem-backed store, which lets me edit and create new blog posts easily.
Oh, and I've also implemented reactions. Not just 6, all of them.
You're welcome to test out comments here, similar to https://github.com/dwilliamson/donw.io/issues/1. I rely on GitHub for authentication (I didn't want to make people come up with yet another password).
(Update on 2020-03-02: By now, you can also sign in via IndieAuth or RelMeAuth. See issue 34 for details.)