I could see Valve implementing some kind of scratch-off lottery, like, match 3 Saxtons without uncovering a Hippy and you win a hat, or if you uncover an Australium Bar, you get an unusual.
It'd certainly be more fun than the crates, and it'd probably sell much better than the keys, seeing as how there's that "OH GOD, I COULD HAVE WON IF I SCRATCHED OFF THAT ONE, I WON'T MAKE THAT MISTAKE AGAIN..." factor.
Seeing as how people got mad after VALVe made Mann co. store bought items craftable after a few days, getting hats and unusuals like that would not only make crates obsolete, but make a lot of people mad.
How about just sticking to metal? Best you can get is refined.