Well I think it would be cool just to make some alternate version of CSS for D3.
Since it is a FPS, we can make characters for admins/mods/ex-staff etc IN the game (Like secret characters which have some powers which regular troops don't. So there is a certain way to access these troops.) Like tracky for example, we have some character representing him, and we put powers on him.
On CSS there are modded servers which have different type of powers, whether it be stealth mode/zombie's/multi jump/speed/vamp etc. But we can incorporate those on the characters representing different people.
I can try to make designs for walls on the game. For example, on CS, you can paint on the walls representing whatever you want, but in my case, I can add D3scene as default in various parts of the map walls and etc.