Wireframe is loosely based on an earlier project called pw-mvc, which has been around since 2012. Pw-mvc was created for a team of developers working on client projects, and is though it's no longer being active developed, it's in use on a wide range of sites, all the way from simple one-pagers to complex directory sites with tens of thousands of pages.
While Wireframe and pw-mvc share many of the same core concepts, one of the key differences is that where pw-mvc aimed to be as simple as possible (controllers being regular PHP files, etc.), Wireframe takes full advantage of class-based architecture, namespaces, and other goodies available in modern PHP versions.
If you're wondering why the name "Wireframe" and not "pw-mvc 2.0" or something along those lines, the main reason was to avoid unnecessary confusion (let alone controversy) caused by the "MVC" part of the name.
The goal was never to produce a true MVC solution, but rather borrow ideas from the MVC pattern and implement them in the way that makes most sense in the context of ProcessWire. Hence "Wireframe".