Security

Virtual Keyboard need to be somehow controlled by KWin to ensure that no input can be injected
Screenshots need to be restricted to KWin. Solution: move KSnapshot to KWin, remove D-Bus interface for Screenshots
Global Shortcut handling needs to be moved to KWin. Easy with kglobalaccel being moved to KWin, but what about non-KDE applications?

Random stuff

Need Video Buffer support, Phonon devs? Requires complete new coding path in compositor.
Usage of overlays (looking into the scene graph, selecting e.g. RGB overlay)
Input redirection (useful e.g. Present Windows, thumbnails)
event to window when it switches the screen (what about screen overlapping windows?)
screen management might need to move to KWin
one framebuffer per screen (requires changes in the compositor rendering path, could be handled in the OpenGL backend?)
XWayland allows us to have TFP from a Wayland buffer instead needing the XComposite. That might be very handy to go to Wayland fast. We can talk to X as we used to be. Normal KWin::Client will do, just needs different TFP path. Might cause some deadlock as KWin would be a client of X and X a client to KWin
PID available thanks to socket, makes killing hung Clients rather simple