I find this so baffling. For me the main positive of WordPress is the UI: it's simple, well-known, well-made, easy to extend.

The main downside of WordPress is the back-end: it's SO limited in terms of the data model. You can't relate objects properly. You can't add meta to taxonomies. I hit the limits of it so often.

Why would you remove all the WordPress goodness and leave yourself a highly-restricted framework?

If you're going to code yourself a front-end, why wouldn't you just use Laravel or Ruby on Rails to build yourself a much more flexible and easier-to-customise back-end for it rather than have to bully WordPress's puny data model and API's into doing what you need it to?