I bet that the revolver is "The Ambassador"
Came here to say that. It could be a sniper unlock, too, his new SMG substitute, because if I understand right, the Razorback seems like it's a melee substitute. Or, if it's the other way around, it could be his melee weapon. Anyway, yeah, every item on that list in the letter has SOME basis in the game, though Jarate isn't in the game (and won't be, I think that's even a little too ridiculous for Valve...they like to play, but the game content itself doesn't quite get that preposterous). So, it stands to reason that the Ambassador could very well be in the game soon enough. We can only watch the update page, and/or wait until the update hits to see. Maybe they're being SUPER DUPER sneaky and sending us something from like the last class to be updated, maybe they just have one idea locked down for that class and now they're leaking it...hell, maybe they just like the name "The Ambassador" and decided that at some point, they'll probably call something that. It's Valve, so who the hell knows.
Edit: I just went to Teamfortress.com about 4.7 seconds after posting this. OH LOOK WHAT IT IS!
www.teamfortress.com The Ambassador, the spy's new revolver. Bravo to all those who guessed it, especially Cut Chem!st for his Peacemaker tidbit. Furthremore, he (Cut) was right about that achievement, the gun silhouette in the achievement picture is obviously the new Ambassador. It's higher accuracy, higher power, same ammo capacity, but (and this is all speculation based on the language Valve used in the update page), much lower rate of fire. Sniper pistol for spy, hooray! Discuss.
