Xephyr is an X server can be run inside another X server as a window. To be honest I'm not totally sure that it could be used to run SurfaceFlinger but it might be worth exploring. VTs (virtual terminals) are what on a Linux PC you would normally switch between using Ctrl+Alt+FunctionKey or the chvt command. It's possible to run separate X servers on each VT should you desire to do that. One would assume you could also run SurfaceFlinger on one of them and switch between that VT and the one running X11. You would probably need to "modprobe fbcon" and would possibly need compile a kernel with support extra VTs too. You can find a keymap here which maps Fn+VolumeButtons to change VT on the N900. It should be possible to do something similar on the N9.