Its kind of a double edged sword in that respect isn't it? By requiring declaration the government implicitly endorses bitcoin as a legitimate store of wealth. Right now anyone that knows even a little about bitcoin knows how to move coins around as they travel.
Indeed, they're paying attention now because Bitcoin already has universally-accepted value. It's not incredibly liquid, but it's liquid enough that Bloomberg and the like have tickers for it.
Regarding the border regulations, I think it's inevitable that the government tries to pass such regulations, if only to deter people from hiding their assets when crossing the border. Many will comply out of fear, and that's what they want.
The fact is that it's not even clear that having access to BTC private keys means that you are "in possession" of the funds. What if both you and your wife have access to the keys (and what if it's a brainwallet?) and you're the only one traveling?
