I kind of doubt it, and I wouldn't be disappointed if it weren't true. We already have nine great classes to play with, and six weapons updates to look forward to. However, while TF2 doesn't really need a tenth class, it would still be pretty awesome if it were true.
It will drive me nuts if it is true because of the changed class selection screen. It's a nice even 3 classes in three groups. If one more is added, the balance of the screen will be thrown off!
As for what I'd like the tenth class to be... Ninja would be cool, but they'd have to do something to make it different from Scout or Spy. I'm not sure I'd like a combination of the two, either. Maybe cowboy, but I'd like to fit in stereotypes from other countries, and we already have three from America.
As for what the tenth action figure could be... A pushcart? The intel briefcase? Pyro unmasked? (I am, of course, of the belief that they will never unmask Pyro. Ever.) Announcer lady? (Hey! Maybe she's the tenth class!) Sentry gun? Either way, action figures would be awesome. I'd totally buy them all.