Ultimately it depends on how frictionless it is to convert it back to dollars, pounds, euros, etc. This has always been an issue for bitcoin. When I first heard about bitcoin, one bitcoin was worth less than a US dollar. I was curious so I tried to buy $50 worth, but the process was so convoluted and difficult I didn't bother. Today its much easier, but not completely so. But much of the difficulty then, and I presume now, was the distrust of banks. The key vendor on their list of supporters is PayPal (IMO). Paypal is in a position to make currency conversion painless for most users. Maybe in the future there will be enough places that accept this new currency that people can keep their money in that form but initially its all about easy conversion.