There’s a good amount of work involved. There’s accepting fediverse comments and storing them, then allowing some kind of reply functionality within the WriteFreely UI and storing those, sending them out via ActivityPub, and displaying them.
There’s also moderation to think about – since these comments would be displayed publicly on your blog, you’ll want to be able to remove any spam / abusive posts, and let other users do that if you have a multi-user instance. That’ll need an extra moderation interface, and/or rules around whether comments are allowed.
Notifications need to be stored, need an interface (which might conflict with our “minimal” design), and then be connected to a mail system to send out an email when you get a new reply. Though this could leverage the stuff being implemented with email subscriptions.
I’d mention another workaround: when you create a blog post, mention your personal Mastodon account. Then when people reply, they’ll also reply to that account, where you’ll get a notification. For example, I might put this in my WF post:
Reply to this in the fediverse: @matt@writing.exchange