Dollar is a popular not just popular but a powerful currency. It is very known world wide. Some country also depends on US dollar, making it powerful, so i don't think it will happen soon. Maybe someday but not so soon.
yes that is right that dollar is too much popular as well as powerful but it is only because of its users, if people will stop using dollar i do not think that it will even survive for some time. in fact the young generation are now changing their interest, most of them are now using online facilities for shopping and for so many other activities. so i am sure that if this trend will continue for a long time then dollar will really become devalue and people will mostly give preference to online currencies.
How would that devalue dollars at all when the online currency that they are using is just the digital version of dollars? And if you're going to say that online shoppers are most likely going to end up using bitcoins, then I'm afraid that's not the case. People have been buying stuffs online for so long now. They are all using Paypal, or they do online bank transfer. Very little of them are using bitcoins. Why? Maybe because bitcoins aren't accepted in any online shop. There are some but they aren't that popular. They are not at the same level as Amazon or eBay.