Realistic and might works but ihmo too annoying for casuals and non-PvP players. I know, know, know this is mmo but we all know most of people scary seeing others in the wasteland. But silencer as additional component for weapons is +1.
Well, yeah, even if you use silencer or melee weapons, the mobs might give out your position... however, another fun factor could be, that randomly that could also trigger other NPC's to arrive, other raiders, or if you are near a town with a faction, a patrol stumbles into you and helps/kills you.
This game needs factions/alignment, as killing a player in a friendly/starter zone, should have server consequences, and safe towns are available for peacefull people and ofc newbies. Only PVP towns and vendors would be available for player killers (outlaws).
Game shall depend on alts less, like crafting shall give no XP and to raise crafting skills, an amount of crafts shall be done instead of spend skillpoints on specific skills.