It will never happen, most people continue to use government currency and it will stay like that. Crypto will always be a minority. I think people become too blinded by what average people do when they spend time on a niche forum like this one.
We also have to consider that many gambler still want to play on a traditional way and of course thats playing online using fiat money. The government will always support that kind of business because they will earn on that, though crypto gambling are also growing I still see this one just an alternative for a gambler who know how to use cryptocurrency.
We know this is only optional and we can't put the other to use crypto and forget fiat since gambling sites are still accepting both of them. Only be happen that all gambling sites will be cryptobased if they will never accept fiat currency. But it makes difficult for some country that never allowing them to used crypto. And with this sentiment, it might decrease the number of the gambler and they'll probably be moving back to offline casino.