That is very interesting idea.As for me humanity isnt ready for that in the nearest future)
Indeed true.
Consider any development, cash or paper money will continue to reign the economy. You can't literate whole country and make them use digital means for every need.
I agree with you. Paper money is a habit. People can not give up this. It's nice to listen to the rustle of the bills. And to make purchases in cash - anonymously
Lets face it Cash is still king when it comes to currency. Yes we all have now credit cards, debit cards, and stuff like Apple Pay but all of which is paid or loaded by Cash and nothing else. Even Bitcoin as a currency is still converted to Fiat Currency because as of right now it still has many uses compared to Bitcoin. I can tell you that if the government has not yet come up with a good alternative to fiat then Fiat currency still has a bright future ahead.
What you refer to in your post is certainly not cash
You evidently talk about digital fiat which is the opposite of cash. Cash (aka "ready money") is bills and coins that you can put in the pocket of your trousers or leather wallet if you have one. Thus when you convert bitcoins to fiat, you convert them not to cash but to digital fiat, which you can then withdraw to your bank account and fill with it your payment card balance. In short, cash is money which you can touch with your hands, see with your eyes and smell with your nose (you can even taste it)