That's where color-coded Minigames come in....(everyone 1 color of player if free-for-all, team color for teams minigame, color can only be used once throughout the whole server.)
You would have to disable avatar customization for that to work and that would be terrible.
It would be nice to be able to have a minigame where sniping is a challenge.
Try fixing the sniper rifle so that it isn't a machine gun.
Sniping was quite balanced in tribes, despite always having a red arrow over your head and a big red line pointing back to your location every time you fired. Being shot by people you can't see is not fun. And you people disabling the names on the server arent thinking about all of the consequences of doing that.
When I make a DM server I try to keep it as realistic as I can; buildings made from 2x2 bricks so you can destroy walls with the nifty remote bomb, vast landscapes and enterable buildings- when you disable names you've got more realism; a harder deathmatch. You could just kick anyone that spawn kills or actions related to that.
Basically, I think the only consequence would be more spawn killers and cheap shots, but since I always host privately, I know none of my friends would do that, therefore eliminating a reason to worry.