Re: crumpled napkins...
"3.8 B per quarter is about 2 chips per soul per year. Is this meant to be sustainable?"
When it's cheaper to put an ARM into (e.g) your toaster than it is to do it with discrete components, it probably is sustainable, given the number of consumer and professional electronic devices in the world, and the rate at which they are replaced.
Whether the replacement rate is a *good* thing, whether that is sustainable, is a separate question.
Toaster isn't meant as a serious example, but I struggle to find a non-trivial consumer appliance in the house, or a non-trivial bit of kit at work (electronics and related stuff, from design to manufacturing and support) which doesn't have at least one little computer in it. Obviously phones, routers, TVs, etc do. Washing machine: yes. Fridge+freezer: maybe. Digital radio: probably. Oscilloscope? Probably. Machine tool? Probably. "Smart" diagnostic tool? Probably.
Or what about cars: what's in the many computers in a vehicle these days? If it needs more power than an 8051, and various regulations and infotainment functions mean it probably does, then what?
Even your PC has ARMs as well as x86s. They're just not so visible.
So, it's probably plausible.