Further to the last post, I felt inspired to tinker and created a proof of concept 'hybrid' blog that uses dynamic pages but builds them on the fly from static markdown post files.
You can check it out here.
In a way, it's almost like a return to how the blog operated on WordPress before switching to (b)log-In – each day is a single .md file divided into sections by an '#' separator. If there are no posts yet on a given day the file will be created with the first post and edited thereafter. The blog page reads the file for the date in question, pulls out the posts and displays them individually.
As with the actual blog, you can click the comment icon before a post to toggle the comment section and leave comments. These are also written to .md files with a name corresponding to the date and post number.
It's really basic at the moment; I haven't worried about organising post and comment files in date based folders, or the logic that would go with that, but it shows how a site like this can be put together. While the post files are created by the system itself, there would be nothing stopping you creating them offline and uploading via FTP. Eventually, I could even devise a system that allows you to upload files via a web UI, checks the date and places it the right location.
There are a few places where it currently relies on (b)log-In's config file and database (only because I couldn't be bothered to rewrite everything) but I'm still surprised by how quickly it's come together. I've even created a separate database-free authentication system which seems to work nicely.
Once I've spent a bit more time on it I may put it on GitHub.