Yes, it should be totally possible to build a blogging system on atproto. And the "app.bsky" API should serve as an example for almost all of the functionality required.

Another really neat aspect of atproto, is that apps can interact theoretically. So you might create a blog system but use "app.bsky" (Bluesky) for comments.

OAuth support is coming soon as well, which is a big step in simplifying auth.