All of the code for quest system is done server side, this has nothing to do with the actual game code. The only thing done in the client is to actually display these quests, which is what you see in the quest interface.
That is inherently different to the actual code of the game, such as in the client, which contains stuff like game mechanics, AI behavior. This code is obfuscated and encrypted in a way that we still until now only have limited knowledge of its contents.
Not to say that it isn’t possible, but things like 6vs6 pvp or 12P may be very close to that. BattleForge was not designed to be a MMO so connecting 6 sessions into one game was already a feat in itself back in the day, developing more slots for players, especially with our limited resources, is no easy task. However, maybe there exists a way to develop 6P PvE based on the existing 3v3 PvP infrastructure.