First of all, the cryptocurrency must be known to more people. Secondly, the national government needs to be recognized, which will speed up the promotion and growth of cryptocurrency. I hope to arrive sooner.
It needs to be regulated by the government first before it becomes a legal tender of payment. As a medium of payment, some people are already using it including me when I wanted to pay my bills because we have a platform wherein we can pay our bills using cryptocurrencies so it makes it easier for the crypto users in our country to do such thing. The scope of being a successful medium of payment may be small for now but later on, it would become larger.
I doubt any government will make a cryptocurrency their legal tender, as they will insist this be their national currency.
Some governments may create a digital currency, not based on blockchain technology, they will designate as legal tender to augment their traditional currency (banknotes and coins).
And, for certain cryptocurrency is being used as a medium of payment. That's not the question.
Instead, the question is what are some of the obstacles preventing widespread use. Crypto payments represent less than 1/100 of one percent of payments in global commerce. I don't consider this "widespread use".
I agree that gaining support from governments for using a cryptocurrency as a medium of exchange is essential to achieving widespread use. To gain such support, there needs to be a collaboration between regulators and cryptocurrency designers so that the design of a cryptocurrency makes it more efficient and effective for regulators to apply their regulations.