I'm surprised to see no mention of postrelational/multivalue databases. Postrelational DBs played in the 80's and 90's, and are still widely used in the world of big iron.
It's historically inaccurate to state we went from file-based databases to relational ones and are now slipping back to file-based ones.
Rather, both the relational and non-relational DB worlds have taken many ideas from the post-relational world (even if not intentionally.)
The SQL/NoSQL + ORM + MVC stack of today is much closer to what postrelational DB's were like rather than what SQL apps were like back in the day. Every generation thinks they invented sex, and high level database programming...