I think is interesting the possibility to modify the game, it makes things more fun at the same time makes the game more popular.
like it >
http://www.gamebanana.com/skins or
http://www.moddb.com/but, I agree that some players can take advantage of it, so have a list of stuffs that could not be modified(like some sounds, textures, gfx.).
maybe, in tremulous, the only sound that the player may have some advantage is walk sound (makes no difference to the aliens, and humans only if they are not wearing the helmet, however, this can be changed if all humans could perfectly hear the sound of aliens walking = no problems with mods).
i like to see more custom models, sprites, skins, sounds, huds, maps and others custom stuffs for tremulous : )
Switch all the wall textures to be semi-transparent, and make the dretch lime green.simple, if the player to change the texture semi-transparent, you would see the image in shades of black(I think this is already happening in tremulous).in short, if you change all images to 100% transparent, you will not see anyone behind the walls, only, all black : )-
the textures were always in a format that does not accept transparence, and to accept, it would not matter if someone modify, the map as they are naturally transparent (like windows or glass).