I really loved both L4D games.  The problem was always pub stomps and people rage quitting if a round didn't go their way.  
I think this may be a good way to "alleviate" that problem (you can still get 4 people who play well together, and then have one person who is a loner).  I like the premise and I'm looking forward to it (well I would be if I still had time to play new games).