Have the silent '[ S ]ilence!' command mute voice commands sent by the player before you for 30 seconds. If you get [ S ]ilence'd 3 times on a map you cant use voice commands untill the next map change. To prevent [ S ]ilence being spammed to mute everyone, code it so that you can mute yourself if you were the last person to send a voice command. This way voice commands will be used more sparingly, the consequences for spamming them will be being unable to use them for 1 minute and then untill the next map change.
Also I feel having a few different sounding 'Ni' commands will enhance the mod significantly.