Let’s assume that stablecoin usage grows massively. Everyone everywhere has easy access. 

People in countries where the currency is less trusted will move lots of money to stables. 

What happens when these less trusted countries lose control over their local currency?

logical step would be to ban stablecoins once usage grows to something dramatic (eg 30%+ in population savings are in US dollars vs locall currency)

most likely scenario is that citizens would be limited in how much one can buy (eg argentina with dollars today) or forced to conduct the business in local currecy only (like in turkey)