After including Christian's patch to allow other clients to unmap windows in mcwm I also added a key to hide windows. Press MODKEY + i and the focused window disappears.
Still no internal way of getting windows back, though. In the little free time I can find I'm experimenting on how I want to do this. I have a small external program that is almost finished that does what Christian's 9icon script does. I'm also thinking about including a menu in mcwm proper, but I'll see about that.
Currently, mcwm never draws anything, not even the borders. It's a feature in the X server that draws the borders automatically. It would be quite nice to keep it that way.
I'll have to think about this...