Maybe cryptocurrency can't replace fiat currency but in a utopic future where money will be only digital or "coined" and cash will represent what originally the bitcoin was made for. Economy and the banking systems had to implement crypto in their asset, but if they'll do it, certainly it will not be agreed by the native users of bitcoin; Anonymus and Instant peer- to -peer transactions are the fundamental basis of cryptocurrencies. My personal opinion is if bitcoin will be globally implemented as an investment asset or used to normale transaction, it will be his death.
First of all, (1) if bitcoin users or who owns bitcoin wants it to speculate over its price, I don't care that a global coin can receive more value than what nowadays already is, of sure the demand, will increase by the users but hyperinflation take his price down again.
(2) If the point(1) is accepted: Why should bitcoin users maintain their assets in their portfolio if the price will fall?
Before responding to this question ( money has the function to speculative, reserve, precautional).
Obviously who owns bitcoin will sell all assets to return to the fiat currencies, which has globally implemented and zero cost of a transaction, and meanwhile the bitcoin will raise the fiat currencies will be the standard. (3) In the end, bitcoin will increase until its implemented ( achieved the higher valuation of all time as a "spike", someone forecast 100x and 1000x) by the way, investor and users will sell all or not at all their asset cause the high volatility of the price.
The future of crypto is to remain crypto also if in long term transaction fees will decrease. But I think that as in the economic circle, the new system takes the old system down and the transistor will be updated by quantum-transistor, anyway will happen to bitcoin if we believe it has to be the future.
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ps Excuse me for any mistakes.
In the future money is going to be only digital.
Now with Coronavirus we are more encouraged to use contactless payments and all is happening with credit cards and virtually.
But due to volatility cryptocurrencies are not going to be widely accepted. Only if cryptos are going to have a stable value of some stables coins are going to be used will save the day.