I've veiwed the Twitter of one of the authers of Left_4_Dead and he had said that he might be making Left 4 Dead 3. The reviews for the game Left 4 Dead 2 was mainly good, so there is no bad comment on creating the third audition in the Series.
I would love to see the new charactors and the new infecteds that they will create if they do decide to create L4D3.
-JacketMatt (A.K.A EvenArtist)