Suboption to "Hide title of windows when maximized" that moves window buttons and title to panel
Basically integrating xfce4-windowck-plugin
into xfwm4
itself. Unity had a similar toggle for title bar in its Appearance dialog.
Panel should be selected either automatically (any horizontal panel that's snapped to top/bottom border, top-side having the priority) or by a user from a drop-down list.