I'm no programmer, so it's more a question and a feature request.
I remember someone told me that there's a GTK feature which has to be implemented in each application to move a window between different screens without xinerama.
But what about that xrandr extension: XReparentWindow(3)
If I unserstand it correctly it should enable xfwm to move windows, right?
XReparentWindow is part of the X core, it has nothing to do with xrandr.
You already asked in bugzilla #4271 and this has already been answered.
*** This bug has been marked as a duplicate of bug 4271 ***