@tux0r I've seen some commenting systems based on GitHub issues. Probably they could be integrated.
But any commenting system which provides triggers and API can be used for what your are suggesting.
Actually, I already have a prototype of comments microservice for one of my sideprojects. Probably, I'll made a SaaS service from it some day.
@svetlyak40wt I would not want my readers to register with GitHub just to comment on my site, and Staticman (which comes close to what I want to achieve, at least) is rather complex and feels unnatural in a Lisp environment.