This is a bit of interface design straight out of the TV series NCIS -- but I figured it actually looked pretty sensible.
I'd like a window manager that's similar to dwm -- i.e. showing one large active window, and lots of smaller inactive windows in a column down one side -- but taking advantage of compositing so that the inactive windows were just scaled down, rather than actually being resized. I'd find this convenient for, say, editing text while watching TV in a window, since it'd be easy to toggle which of the windows occupied the main area while having a reasonable overview of what's in the others (although doing that efficiently would require integrating the XVideo extension with the compositor).
It'd also be useful to have a keybinding that'd make the active window occupy the full screen, completely hiding the inactive windows, and I'd like to be able to show more than one "active" window in the main area (say, two side by side). Actually, why isn't there a good scriptable window manager framework that'd let me write this sort of thing in a high-level language without having to implement all the compositing stuff myself?
Donald Stewart wrote to point out that xmonad is almost the window manager I'm after here, and since it's written in Haskell it's ideal for me to play with...