It looks pretty awesome to me. Looks like you can go into some of the levels in the game and choose any 1 to 3 people in the game and mark them as targets. You can also decide things like what disguises you start with and what weapons you start with and so on and basically upload the "contract" online and your friends can play them.
I think this is a pretty cool idea. Admittedly it seems a little simple and I'd want much more options like how the targets behave and where you start in the game and so on, maybe even the ability to customize maps by adding objects/people/weapons/etc but this is a great start. I think this could add a lot of replay value to the game, especially for a game that doesn't encourage a lot of replay after you finish a level. I know the hardcore fans like myself will go through levels trying to finish them in different manners and using different approaches, but the casual fans will stick to 1 proven and tried method if they replay a level.
With this addition I feel like it'll keep things fresh. I always liked creating my own backstory to the missions and going out of my way to kill certain people in the older games, so this will make it pretty interesting.