As far as I understand, currencies have value because we all agree they do (or because there is a guaranteed fixed exchange rate for some other asset that we have all agreed has value). The extent to which a currency is a good store of value will be determined, again, by how many people believe it is legitimate and continue to accept it for transactions (though fiat currencies have a wrinkle where a central bank can produce an unlimited amount. In this case, the fiat currency is a good store of value to the extent that people believe the central bank won't do this). I don't see why there is any reason to believe that a digital currency could not succeed if enough people believe it has value.