They should definitely make Sleeper an option, If they did, players that want a good raid, and are okay with being offline raided can do so, and players who just want to play the game casually can do so. Maybe they could call it like, "Rust Hardcore mode" and have increased zombie spawn rates, better drops, etc.
Wait a second... It already has a name, sleepers, why call it hard core mode? Also generally in games hardcore modes do not have increased drops, and increased spawns(in this game more zombies would just be easier to get more lootz.) So what your describing should be called softcore mode?