If fiat currencies change into something like cryptocurrency, then probably crypto will lose its novelty and people will prefer to still use the fiat which has been digitized. Since the fiat will be supported by the country that created it unlike crypto which has always been frowned upon by the governments.
I think there is a positive effect on this. Remember money being recorded on blockchain? Corruption will then be decresed since all the government expeditures and incomes are open to the public. These money will then be used to where it should be and not put on the pocket of this corrupt officials. This is the reason why cryto is being frowned upon by the government officials. Due to its transparency.