If it's just challenging then it already has been achieved. But replacement currency may not be achieved because we are still under a government. If the No. 1 currency will be toppled over, it will be replaced by digitized fiat.

BTC will be bigger in the future maybe 50 years from now if this is just another goal that you can look at.  1Million per coin might even be achieved which is a reason for banks to also accumulate BTC.