I'm sure many of us wanted to continue with the Dark BrotherHood and keep assassinating people, just for Roleplaying purposes, but in the end you'll find out, theres no one left to kill.
I propose a new idea, why not make the game randomly generate NPC's once we want to assassinate someone?
My idea: Since some of you want to continue with the Storyline, you could talk to one NPC for Assassinations and the other to continue with the DBH Storyline.

There is a http://www.gamesas.com/index.php?/topic/1150214-the-dark-brotherhood/ to continue your assassinations discussion. Thanks.