I played BW mod online a little and i noticed one thing: any players vs players gametypes kill the whole awesomeness of this mod.
Everybody chooses one or two weapons that cause the biggest amount of damage in the least amount of time, so 80% of weapons stay unused.
And i think that there's only one way to force players to play with all weapons: coop where you need to kill computer-controlled enemies to earn points and buy new weapons. It can be invasion- or assault-style gametype.
How about this idea?