It would be interesting to have some autonomous bad guys that would attack online players at random. Imagine, for instance, if there was a roving horde of zombies, that attacked at random. Say once an hour, the game would choose a player at random and attack him. He would be sent a PM that he was under attack and would have 'x' amount of time to log in and mount a defense. Traditional defenses would not be very effective against these guys, but there would be some things you could purchase and have onhand to defend against them. If you did not respond to the warning PM, the attack would happen against your default defenses, which would operate at a disadvantage. These attacks could hurt someone, but not take them out. If you successfully defended yourself, perhaps there is something of importance you could take away from them. What do you guys think of that?
Can you imagine someone interrupting a meeting at work or something, because they just got a PM on their phone and had to run to fight off a zombie attack?