And if the use of cash can be reduced in society with more other options being used by more people, I think cash could really become waste because very few will use it for anything. But because currently many people still use cash in life even though there are other options such as gold and Bitcoin, I will not immediately consider cash as waste because I can still use it to buy things that I need in my current life environment. However, I also wouldn't be surprised or deny this if it could actually happen to cash in the future.
What do you think will really change after that? If a country reduce the cash by 70% and let the 30% available for rural areas since they likely don't have access to the internet and allow the rest to go digital, will there be difference between what cash is doing? I don't think so, inflation will remain the same because the supply of money will remain but this will allow the country to be able to track money easily and also block some.
The only benefit of going digital is that the central bank will not spend money on printing again but even if they stop funding printing of money, that money will go to improvement of digital payments and frequent update to make the cashless to be faster, clean and easy for everyone to use.