The probability of each event happening is high enough. But the probability of all three happening at once is low. And that is why this prediction is difficult to believe.
I think it is true windows dev is much more difficult now. The platform has an identity split. It used to favor power users. Now it favors the rich mac users. And upcoming kids who are attached to iPhones. And this means… it gets worse … Or it changes audience. The latter will be hard to pull off.
I think Microsoft also has less need for windows. We know this because its core business has been shifting. They are platform agnostic now.
So what becomes the incentive for Microsoft to continue windows?