Step 1 is to get everyone access to internet. Facebook and SpaceX are already working on it, so it can't be long anymore until everyone has the possibility to go online.
Step 2 is to get everyone the hardware to use cryptos. Chinese mobile phone manufactures are leading in the cheap phone section. Shouldn't be too long anymore until everyone can afford a smartphone.
And the final step would be to increase the knowledge of cryptos all around the world.
So in conclusion bitcoin is not ready to become the world's number 1 currency. The earliest step towards a fully digital economy is that internet access and electricity can be enjoyed by all people in the world without exception. You can imagine without these two things how someone could use their cryptocurrency. In addition, we must remember that bitcoin is outside the existing economic system. For entities called countries, bitcoin is considered a virus.
If we study the history of fiat money, we can find out why the dollar has become the main international currency, because the creator or controller of the world economic system who made it, of course, with a series of tricks and intrigues with the aim of benefiting the controllers of the world economy ("the have" group) and making wealth. Maybe the period of fiat money (physical cash) will end and be replaced with cryptocurrency, but the cryptocurrency that will be used is not bitcoin but that created by the controllers of the global economic system.