me and Lionel Chauvin are working on bringing appmenu support to KWin.
First, there is kded-appmenu, a kded module needed to enable multiples applications (krunner, kwin, ...) to import menu at the same time.
And then this kde-workspace branch:
Here a video showing how it looks:
We hope this in KDE 4.9.
Here the patch for KDE 4.8: