Well, the existing value in Bitcoin, for one. I'm mining dogecoin largely to learn a little bit about these currencies, but if everyone did move over, by the time it reached the same value Bitcoin has it'd be regulated too.
From what I've read, I doubt the Japanese government (mostly Aso, whose game I'm guessing this is) actually understands that there are other cryptocurrencies.
Similar to "bath salts," that legal trickery may work for a while, but the law will eventually catch up if a government is motivated to stop something.
From what I've read, I doubt the Japanese government (mostly Aso, whose game I'm guessing this is) actually understands that there are other cryptocurrencies.