Does cryptocurrency have anything to do with religion? not related! Muslims also contribute to humanity and they accept cryptocurrencies.
Of course it can be allowed and used in Muslims countries without any doubt. In fact countries with the biggest markets for the world have a majority or a certain portion of Muslims. I see the technology spreading to Middle East in the near future. Besides, there might be an argument that cryptocurrency is not allowed according to a particular concept of a particular group which could be avoided or not taken in to concern for ultimately if there is demand for it, there will be supply.
if fluctuations are constraints that they consider, their local currency is also vulnerable to inflation right? I think it is clear that what is forbidden is to use the currency for gambling or detrimental activities, even though the Islamic countries themselves more prefer to the dinar (gold) currency as the main currency because it is much safer and more stable