"US$ Travelers Checks will be perfectly fine for this reason. "
Those count for the $10k too. You'd still need to file the form. The better question is what exactly do they do with it? The amount is also tied not tied to the rate of inflation. In another 10 or 15 years, it will start to be bothersome to more people. It's surprising that the tin foil hat wearers in the security forum aren't making 1000 posts on this every day given that the government is trying to control the movement of people and their money.