This might be an example dependig how balanced the new character would be. If it was so overpowered that you had to play the new character yourself to not being bashed all over the place by other players, it would be almost like forcing everyone to pay $10 to continue playing. Now would you want that?
Actually, the TF2 example is an example of the wrong
kind of paying structure. It's a perfect example of how games are not Legos where you can freely remove one piece and the rest stay put.
Every piece in Chess, even the Pawns, are vital. Chess as a game doesn't work if you have no Queen from the start. And Chess is fundamentally unbalanced if one side starts with a Queen and the other doesn't. TF2 is very much like this.
Every class in TF2 exists for a purpose. They are imperatived
. The Pryo's primary designed purpose is to kill clusters and kill Spies. If there was no Pyro, the game would be unbalanced in favor of Spies. If the Pyro were a class you had to pay for, then the success or failure of your team is based on how much they're willing to pay for the complete game.
Or, if there was no Pyro, Spies would be significantly nerfed from what they are now so that they would be properly balanced. So, if you add Pyros, then it now utterly owns Spies. Unless they improve Spies to their current levels, thus forcing
you to by Pyros.
TF2 is not something you can just take bits away from or put more bits in. It is a balanced, competitive multiplayer game. The casual player may feel that you can just slap some extra stuff on, but anyone who is even remotely serious about the game knows that everything exists for a purpose.
Adding a new TF2 class is like having the deleted scenes added to the DVD release of a movie. More often than not, the movie is worse off for having the extraneous material added. Even the Lord of the Rings extended editions suffered from this for a couple of the added and extended scenes.
Plus, there's the fact that this is a multiplayer game. If you add a new TF2 class, it must also exist for a purpose. That is, like all other TF2 classes, it cannot be superfluous. That is, there must be some tactic that this class is designed to stop which cannot be stopped by normal means, or this class must enable some tactic that would otherwise be impossible. Which means that multiplayer balance is destroyed; you're stratifying the playerbase. There are people who have the new class and people who don't. And the ones with the new class are going to be fundamentally better off in multiplayer than those who don't. It's this fundamental fact that killed off EA's ridiculous "Purchase Guns" nonsense.
Honestly, what concerns me the most is that the lead game designer for a major PC game release is promoting a concept that is clearly antithetical to good game design. Maybe it's his CEO nature overriding his Game Design sense.