I guess the bitcoin will turn to be some kind of virtue GOLD, and there will be a lot of virtue CURRENCY based on the bitcoin, like USD based on gold in 1944-1971.
There will be some guy claim that they promise to buy back the CURRENCY they issue with a decided rate, just like US Gov claimed in 1944. And if:
1) Their CURRENCY is more convenient to use than BTC;
2)They have lots of BTC at first;
Their currency will start to be more popular than BTC, and later, they will:
3) issue more CURRENCY than the BTC hold in their hands at the decided rate.
but making fake currency of BTC is not a crime, It's really easy to make fake papers, right?
If someone need online spend, they won't need currency of BTC, they can use BTC directly, for ofline cases there is no way to verify the currency (fake of copied).....