I've continued to idle with more fervour since the latest update. I now have 97 items, 4 of which are hats. You can actually see people's backpacks now, mine is here. I can't imagine why you would want to see it, but it's there regardless.
The real question is what item crafting will look like. Since they gave us backpacks with 100 slots, I imagine that it will take a lot of items to craft a hat. After all, if you have a full backpack, you're probably going to have at least 5 of some item. Personally, I have about 30 Dead Ringers, and 10 KGBs. (It's funny, I like the Dead Ringer, but the instant a GRU [A delightful pun] becomes available, I'm never going to equip a KGB again.) So, if you need 10 duplicate items, it will take a little bit of focussed idling to craft a hat for most. If you need 50, less than 1% of players will be able to immediately craft a hat. If the crafting coincides with a trading system, that would make it easier; players could congregate and create piles of 50 by tactical trading. I can't imagine they'd require more than 50 items. Regardless, this still means that there's no trade you could reasonably make between hat and non-hat items. There's no reason to trade 70 items for a hat if you could just craft one with 50, and the other player wouldn't want them if they weren't easy to craft with.
My only real fear is El_dawg's prediction: that you'll only be able to make Spy hats out of Spy items, and so forth. That would be doubly disastrous: firstly, most of my items are spy, and I don't particularly want another spy hat. Secondly, this would mean that no one could craft Demo, Soldier, and Engie hats. (Really, I'm just talking about Demo hats, which are the best hats in the game. I saw a couple people riding Top Hats yesterday, they look so good.) I have the Stainless Helm, but I'd prefer a Tyrant's Helm.
PS. Best Heavy Run in my life: 44 points. I stuck with the cart the entire way across Badwater, except for a brief excursion to the roof above the second Capture Point.