Hats, crates and keys and possibly a map. At this stage, I wouldn't be surprised if there aren't any more weapons with unique stats..
They better do something big, we have been waiting for weapons too long. If they add 50 moar hats and not a single weapon, many people including myself will be very disappointed. Hell, it doesn't even have to be a weapon. It could just be a upgrade or something new with weapons that drasticly changes the game-play such as the new MvM reviving system with the Medic.
I doubt it considering the new update they just did with the medic they wouldn't want to be too biassed towards one class.
New invis watch stats- Cloak lasts 150%-200% longer but can only regenerate cloak by killing an opponent. Almost like the black eye skull effect from the Halo games Done. Now valve choose a model please