I don't think any country's central bank would have much luck with crypto's as there will probably need to be inbuilt restrictions and tracking information, making people keen to hold onto BTC. What will kill bitcoin, if it is not a systematic crackdown by the US government, will be people's adoption of altcoins, specifically litecoin. Bitcoin confirmations can be a bit slow when compared to litecoin, which might one day be the deciding factor for a slow and steady transfer of wealth from the former to the latter.