Serious question: Have you used Wordpress before? For what it lacks out-of-the-box 9 times out of 10 exists in the form of a plugin (sometimes multiple plugins). I don't see what Wordpress lacks personally other than a coherent file structure and clean codebase...

I'be be much more interested in a new modern, flexible CMS built for that purpose from the ground up than I am about a new blogging software.

Sounds like you're talking about Drupal here or ExpressionEngine which are both great and well-written content management systems. Wordpress serves many purposes, clean code doesn't matter so much at the end of the day unless you're a code purist who thinks languages and conventions matter if the end product works and is usable.