any real MVC library in PHP (for GUI apps)

[Not an answer. Just wanted to remove this from the question, as it's only related, not a solution.]

There is the PHP interface preprocessor. However it is very simple and low-level. It provides an output interface for Gtk, as well as ncurses, but also PDF or XHTML serialization. Which is interesting, as it's close to real MVC constructs in allowing to exchange the View for different backends without adapting the Controller even. But then it only provides the basic widgets, and not a whole lot of simplifications. Thus I only consider it related to my original question. So, a side note.