Bwahaha! That's a joke right? The PS4 is still outpacing the PS2. Sure, I don't think it will last forever, but 100M is a given. Sony actually lowballed their shipments for this fiscal year, so it'll probably be at 80M by March of next year. Before 2018 is up they'll be past the PS3's ~87M. Sorry, but it is going to pass the Wii.
Yeah, I really don't understand why Sony sees the PS4 dropping by 2 million this FY. It's the first full year with the Slim and Pro. I can see it remain flat.