NPC factions can be joined by players, and in my opinion npc factions should be separated from player factions, and one player could belong to both npc faction and player faction. Belonging to npc faction would strongly improve PVE, because in PVE you would get real good bonuses for PVP. And for that it should be made, that players couldnt leave npc faction once joined.Vault city faction members - which are high in vc ranks, should be able to buy permenant combat armor implants like in f2.Brotherhood of steel members - which are high in BH ranks, should get ability to access one of those: brotherhood armor or pulse rifle or implants of strength, perception, charisma, intelligence like in f2 http://fallout.wikia.com/wiki/Red_Memory_Module .Enclave faction members depending on rank should get access to one of: vindicator minigun/apa/apa mk2/power armor/hardned power armor. All power armors could be gained in certain time period, for example every once a week, and they should be unlootable after death.Raiders faction - should have some good way in caps making, since robbing people is what they do.Unity faction - should get the ability, to get floaters/centaurs as companions. Or make some trades for mutant skin and like +150hp/some resistance and inability to run as a tradeoff.But that would be only bonuses in PVE part, there should also be npc fctions pvp part. While raiders are enemies with vault city and enclave-bos-mutants are like enemies between each other there should be some regular npc factions pvp every some time. for example, lets say every thursday 18:00 some repeatable event should happen, for example: where raiders would attack vc caravans, and every vc citizen could go to some exact place in world map to join their city and defend the caravan against raiders, while players belonging to raiders faction would join same exact place to help raiders successfuly rob vc caravans. Same should happen between enclave - bos, bos - unity, unity - enclave, and the taking part in such events would increase your rank in npc faction much more than doing stupid quests. Number of people who can take part in such events should be limited, for the events to be balanced.