I was just thinking, this way, over time, you could get to know other people's Arch Nemesissies easier than all their alt's Nemesissisis due to people can only have 1. I would put more time into 1 Arch Nemesis vs. all my alt Nemesisisses, too. Plus, it throws in some randomness in encounters and for loot for a well known part of the game - Nemesisses.
What a great idea, huh?
Plus I already have mine picked out. He's called 50/50 or 50/50-man. His special power is to cause a guaranteed fail on all things that have a 50/50 chance.