Vietnam is not the cash cow, most users are prepaid on plans...

Vietnam is not the cash cow, most users are prepaid on plans less than $5 a month. The whole buy phone and get 24month plan like Aus doesnt exist here. So the majority of people utilise wi-fi as it is literally everywhere. They do love mobile phones though!
Most common thing in Vietnam to do is go for coffee - which comes with free wifi. So no real data plans required.

That said .. the burgeoning middle class here does setup potential for future growth, but I wouldn't be expecting dramatic numbers. Australia is most likely the best place for this tech as it has s shit wifi network by international standards, therefore you need data.