I think I found an easter egg, but it might have been an effect from a server I played on.
This happened a while ago, back during the days of the 2.5 beta client.
The game's sound was replaced by people's voices. When somebody took the flag, an excited voice said "I got the flag, I got the flag!" and when you shot somebody, you hear somebody's voice say "Boop" to imitate the damage indicator.
When you the nex, somebody's voice said "Shooo" and lots of other sounds were replaced too.
I lol'd.
The effect lasted until I closed out Nexuiz. The effect was still there when I changed servers, but once I closed Nexuiz it never came back.
Was that an easter egg, or what was it?