So, I am bored, so it must be rampant zero evidence-based speculation o'clock.
The Polycount Pack, wot is also bringing trading with it, has a whole bunch of items, which Valve have said they're going to assign some nice, game-breaking attributes to, hooray!

Clearly it's the job of bored insomniacs such as myself to provide rampant speculation on what those game-breaking attributes might be. And you. Yes, you.
And then it's the job of slightly better informed opinionated nerds to tell the first lot that they're talking a load of gnat's testicles.
So, opinionated and subjective reasoning away! I'll go first. (Details and pics are
here if you've been living under a cyber-rock.)
Scout - Special Delivery KitShort Stop: Looks suspiciously like a pistol with four barrels. Perhaps it's a similarly foolish and dreadful thing as the FaN, you can fire all the shots off very quickly by holding left click and they have knockback and are annoying and everyone on the internet will hate it, but it's practically useless.
Mad Milk: Looks suspiciously like a bottle of milk. I'd suggest it makes you "moooooove" faster. At the cost of, er, I dunno... having blurred vision or something? (note the particular silliness of this suggestion)
Holy Mackerel: Looks suspiciously like a mackerel. Much slower swing speed, bigger range, bigger damage, more comical sound.
Milkman's hat: Looks suspiciously like a milkman's hat.
Soldier - Tank Buster PackBlack Box: The antidote to Derek Hit. Holds 1 in a clip. Fires a slow, arcing round that has massive splash and is great against buildings. Makes you rubbish in a straight fight.
Battalion's Backup: I'm at a loss here, so... makes everyone around you move 50% quicker. Charges up the same way as the normal thing. (worst suggestion so far, probably worse to come)
Hat: Looks bad, I don't want it. TF2 needs fewer train drivers.
Pyro - The Gas ManAside: Conspiracy theory to get Gasman back playing TF2 again.Power Jack: No random crits, applies a new, more annoying damage over time effect called "Electricity Damage" or something equally inventive. Ruins lives.
Degreaser: Removes grease from teammates' faces. Also burns enemies. Really I don't see what this will do differently.
Hat: Looks bad, more pyro "comedy gold".
Sniper - The Croc-O-Style KitDarwin's Danger Shield: Makes a backstab only hit you for normal damage, breaks after one stab, doesn't stun the spy, but gives everyone mini-crits on him. Like a Jarate trap made from leather. Sensible.
Sydney Sleeper: Applies new, previously discussed (in Scout bit) annoying blurry vision effect and bleed damage over time, makes several career heavies have mid life crises. Does lots less damage. Is annoying but useless.
Bushwacka: Looks better than the standard knife. Crits anyone who is under the effect of annoying blurry vision time.
Croc hat: Looks amazing, want want want want want.
Spy - The Saharan SpyEternal Reward: Every backstab re-charges your cloak meter, according to how much health the guy had when you stabbed him. No more refilling each watch with metal. With C&D, just temporarily increases recharge rate after stab.
L'Étranger: Does no damage. Instead applies random game effect to any enemy hit, including fire, blurriness, invisibility, ubercharge, even death! Quickly becomes most commonly used 6v6 weapon. (this is by far the best idea in this whole post)
Fez: Love it, even with the glasses, just looks cool.
Right, those were my incredibly stupid thoughts, I want to hear (a) why mine are wrong and I can go jump off a cliff after screwing myself with a cake fork, and (b) your incredibly stupid thoughts, so I can provide part (a) for you. That's what forums are for, you know.
Gogogogogo!