I'm not certain, but I think over time, some form of cryptocurrency will replace what we consider paper money. Nearly every major bank has begun to explore the possibility. Most governments are at least talking about cryptocurrencies. It will be interesting to watch over the next few years if the cryptos continue to operate as truly independent currencies or if they are somehow co-opted by governments and banks along the way.
Before someone comes along and says, "Bitcoin can't be co-opted", don't bother. I realize that. But a government could easily start their own currency based on a blockchain and then use that as their only authorized digital currency. I'm certain some governments are already considering it fairly seriously since there are nearly weekly comments out of both Russia and China to that effect. I would surmise, the current governments are just trying to figure out how best to "roll-out" the new currencies in the most effective way for them to maintain control.
Thank you @bigpanda finally an answer I can understand and relate to. Maybe the cryptocurrancies will become legal tender but it seems that each government will want a form of their own currency so in theory it could be like the dollar or pound or yen - one they have control over
Exactly. I think this is what will happen over time.