The combined sales of the PlayStation 4 and Xbox One could total as many as one billion units, suggests Microsoft Interactive Entertainment Business senior vice president Yusuf Mehdi.
Speaking with the Official Xbox Magazine, Mehdi said his company isn't done with the Xbox 360 yet, and that he expects the old and new consoles to grow side-by-side for some years to come.
"We believe over the next five years we can break a 100 million unit installed base," said Mehdi.
"That's something we're shooting for, it's not a financial plan as such, it's just rough numbers if you will. To sell another 25 million, half of those will probably come from replacements, but half will come from new buyers."
Mehdi explained that continued growth on the old console would be supported by "hitting new price points" while expanding the range of entertainment options available and reaching new customers.
This suggests that Microsoft could be adding some of the entertainment features seen during the Xbox One unveiling to the older console.
If that's the case, it doesn't mean that Microsoft is any less sure of its success with the new Xbox.
"Every generation, as you've probably heard, has grown approximately 30 per cent," said Mehdi.
"So this generation is about 300 million units. Most industry experts think the next generation will get upwards of about 400 million units. That's if it's a game console, over the next decade."
For Mehdi, the expanding entertainment features of the PS4 and Xbox One mean that consoles aren't just for gamers any more and can have a much wider appeal than that supposed by the "30 per cent" rule.
"We think you can go broader than a game console, that's our aim, and you can go from 400 million to potentially upwards of a billion units," he said.
"That's how we're thinking of the Xbox opportunity as we go forward."