This is actually not on handwritten.blog, but on the site of the person where I got the original idea from! Maybe I can incorporate something like this on handwritten.blog too (e.g. a way for people to send in comments via email).
https://tuhat.net has comments via email, but only when responding to a newsletter post. Then the replies are put in the authors letter inbox connected to the post. Though all comments are private to the original author.