Bitcoin is not possible to be the main currency. because indeed if we look at this it is not possible with fluctuating prices and also very risky. but with the blockchain later it can provide a new thing that might also be a digital payment option.
I agree with you that bitcoin will not be a major currency, because besides the price is not stable, there are still many countries with low levels of public education so that it would be difficult if using bitcoin. Besides that there are still many internet networks that are slow.
But if this is an alternative currency, I am sure it will be usable because this is a reasonable choice for middle and upper class people who have mastered technology and already established economic levels.