Single digit margins on $14 billion dollars in quarterly sales is still lots of money. 2.5%, as an example, is 350 million dollars a quarter, which is still 1.4 billion dollars a year.
I fully expect it to never come. I don't think it really matters. Amazon will continue to take market share off physical retailers, expand its product range and push into new markets.
That day may never come.
edit: Every quarter with margins in the single digits is additional evidence that it won't.