an idea i have is that servers use ace of spades like a build engine and use custom changeable skins, models, game mechanics, everything etc.
for example a server called "halo imitation"
would have halo models and guns that are stored on the server and are downloaded when you join the server into a temporary folder in Ace of spades folder.
as for game mechanics the server could have a different fog render differences, extra weapons, lower gravity, walk speed, jump distance, new vehicle, block damage, A.I bots, basically anything you can think of within reason
it would work like how you would mod mine craft, by removing/adding files to the game libraries to change how the game plays. i know servers now have some mod ability with scripts but cant change the basic game mechanics and such but this would make ace of spades completely mod able.