if tf2 would EVER make new classes, chances are they would need an entire new group, (offense, defense, support) or they would just add a class to every group.
im afraid tf2 will become a game where you need to make hard decisions about what weapon to use. because tf2 keeps growing and growing, and soon every class will have 20 weapons. hmmm...revolver? ambassador? stun gun? nerf maverick? grapple hook? (would be teh love :D)