Probably entrail reading, which is more applicable to the games industry than divination. That, and the 30 years of console sales patterns to draw on.

Huh?

Look, I guarantee there's a game shop in Small Town, USA, right now with more Xbox One consoles on their shelf than they'll sell in three or more years. And I guarantee you'll find "new in box" Xbox Ones on Ebay 8-10 years from now.

Even if Microsoft stopped producing new Xbox Ones this afternoon, it wouldn't magically make those ones disappear.