Had an idea for assasination type missions, and i was thinking that perhaps they could work something like this:

If you do choose to join whichever shadowy society in Skyrim happens to be the assassin one, then aside from the main quest for that faction, there could be a weekly random assassination/repeatable quest that makes use of the radiant story feature.

So for example the game could keep track of certain characters, non important, expendable ones, like innkeepers, store owners, even random citizens, and then they could randomly become the targets once you accept the quest, once they are dead the game could just randomly generate a new npc to take their place some weeks later so that the world never becomes empty.

You wouldn't have to travel to the guild headquarters to take the quest, perhaps a crow could be sent to you on some occasions wit the mission wrapped to its leg, signs on trees may alert you to a damp soggy note buried at its foot, or certain inns may have shady characters with a special message for you from the guild master that then leave quickly once a piece of paper has been pressed into your hand.

The other thing is they could be ignored completely if you didn't want to do them, and as i say this would have nothing to do with the main quest chain for the faction, but rather just a side show to wrap you up on the role of assassin even further, what do you think any good?