It's possible maybe 5 years from now, gambling operator will find out how good Cryptocurrency is and they will integrate it to their system and it will become advantageous to operator and gamblers, it will only happen if these gambling sites that are based in Cryptocurrency will succeed and so far it's succeeding so we'll see, it happening five years from now.
I think you are right, considering how highly loved and famous cryptocurrency is at the moment, we won't be speculating wrongly if we say fiat would be totally eradicated in few years which I believe 5 years is even a long time for this to take place. Cryptocurrency gambling is quite safer and also gives more profit especially when there is a bull run.
Even the casino owners are now are that gamblers are more interested in playing with crypto than fiat, so definitely in few years the owner of fiat gambling site would find a way to convert it to crypto site or even create new gambling sites to meet up to the needs of players. They have to follow the trend if they wish to make profit.