Doesn't make any sense TBH. We should've seen it starting to replace conventional currencies by now.
We are not seeing it as a currency for the same reason that we are not seeing gold coins or Apple shares as a currency.
Bitcoin isn't a currency. It is a highly mobile commodity. You can pay in bitcoins but the seller actually wants $$$ , not btc.
All three come close to a currency, bullion coins since millennia, Apple shares just since some decades and Bitcoin since years. People recognized their value! Just to "replace" a currency you would need to apply lethal force. Something "official" in the workings.