@daviwil There is a nice article about possibilities with ActivityPub and pure static site generators:

https://s3lph.me/activitypub-static-site.html

I'm not sure if it possible to maintain comments only on external servers outside the blog. Probably there is some nice trick, which can make it possible using frontend webserver like nginx and bunch of configs for it, but I need to explore ActivityPub deeper to answer with more details.