Anonymity and popularity of Cryptocurrency are two of it's the best attraction.
And Cryptocurrency games are more transparent.
Will, there comes a time that all online gambling sites will be Cryptocurrency based?
It highly depends on the country but most online gambling websites that I know require the supplement of KYC in their registration.
To answer your second question, I think the time that all online gambling sites will be Cryptocurrency based once we shift the medium system to an electronic type of cash. But for the time being, it is impossible that it would happen anytime soon. The fiat system will always be present no matter how we change the medium.
That will happen in time, i also believe on that but maybe online gambling sites will still accept fiat money and they will choose to accept both currency because they know some of the gamblers are still prefer to use fiat money since the value of cryptocurrency will tend to increase year after year.
Using fiat maybe but not on online gambling casino. I wouldn't bother my self to linked my credit card into the gambling site because there is a possibility that I was got hold by the bank because of gambling sources. I still prefer using cryptocurrency as a form of money on the internet. Time to time bitcoin casino will always be pumping in the gambling industry and that is expected. And all gambling online casino will be based on cryptocurrency.
The only time that cryptocurrency would be the main medium in online gambling sites is the time when we shift our system of payments, which is impossible for the time being. There are countries who lack access to the internet and other relevant stuff to cryptocurrency. Despite this shortage, making cryptocurrency as the main medium is potentially dangerous to the economy.