Well, to demand a ransom in cryptocurrency while committing various crimes for criminals is still very convenient, especially in coins with a high level of anonymity, such as Monero and others. With the spread of cryptocurrency, most likely, the number of crimes will also increase, where cryptocurrency will appear as money. In many ways, its use in the commission of crimes will depend on the effectiveness and extent of its regulation by states.
We should not pay much attention to this issue, because the development of new technologies should not depend on the fact that it can be used with bad intentions. With the help of cars, many crimes are committed, but no one is going to ban them.