I think about implementing comments over kirby pages.
The user will get a form in the frontend. Submitting this form will create a new comment-kirby-page in the backend. This comments folder can be for-each’ed.
I like it. Nice simple approach, and should perform just fine in the vast majority of circumstances. Kirby’s performance drops when you get hundreds of subpages, but that’s an extreme edge case for comments.
Two things to consider, which you will have to either write yourself or find a framework for:
Authentication / spam detection
Moderation (approve comments before they’re published) and flagging/reporting abuse