But that doesn't necessarily mean that cash will go away, I think people are attached to cash a lot and it's a different feeling when you have cash.
In my opinion, your opinion is true. Why ? Indeed, cryptocurrency is now much interested, some people consider cryptocurrency as a valuable asset to them. but cryptocurrency has one weakness that is not the official currency. cryptocurrency is just a virtual currency in the digital world. so this is where another function of cash is to be a medium of exchange for cryptocurrency, so the selling value of cryptocurrency can be used for in the real world.
I don't think it's minus for a cryptocurrency. I remember how electronic payment systems used to be for example Alertpay, Paypal, Solidtrustpay and others. All of them were also considered illegal before, and people did not understand how to regulate them. But then came up with their verification via credit and debit cards. I think that some ICO, with the best product, will soon lead over Visa and Mastercard/ Thus the issue will be solved with the legality and legitimacy of the cryptocurrency. The only question is when it happens.
There is no doubt about it, since crypto is at its infant stage and still it wasn't matured enough at this rate. Regulation of cryptocyrrency will also come at its right time, but as of now there are still some things that it needs to develop before it goes to the peak, so while it is still at its development stage let us just support all the way to the top.