I will use a cryptocurrency as an actual currency when actual regulated banks support current accounts, savings accounts and make loans denominated in said cryptocurrency. I mean, if it's a valid currency that works as well (or better) than pounds, euros and dollars, why wouldn't they? Bank accounts are far safer from fraud and hacking than raw crypto, and transactions can sometimes be reversed where you've been parted from your money by a criminal. So overall this would be the best way to access crypto, you get the advantage of the alleged freedom from inflation without all the disadvantages.
If you know the history of money, and the role gold played, you will understand that the banks will be able to support account balances of many, many times the actual amount of cryptocurrency in their possesion. Commercial banks will be able to add additional current account crypto into circulation in exactly the same way they currently create pounds/euros/dollars "out of thin air." (Long story short: 97% of British pounds in circulation are the creation of commercial banks, money is created when they make a loan and destroyed when the loan is repaid. Interest rates and customer demand determine aggregate level of loans outstanding, hence amount of money in circulation.)
Once everyone has confidence in the new deposit account crypto, we can quietly drop the requirement for banks to actually own any, just as we previously dropped the requirement to hold gold, and just control the rate of money creation using central bank interest rates...
No, wait, that means we're back where we started!?
Whoever invent Bitcoin did not really understand money, there's a reason we went off the gold-standard. It's not a good thing for the money supply to be fixed, money supply actually should expand and contract with the economy. (That in addition to the faults listed at the start of this post.)