This all stemmed from a controverial post on Quora which stated, right up front:
Apple will create an iPhone primarily from ZrO2 - Zirconian Ceramics
Greg manufactures things for a living; I use his Luma Loop camera strap every time I pick up my big camera. He tends to know what he’s talking about, and uses much of the same equipment that Jony Ive does. Greg writes:
Apple is a hardware company and machined aluminum is their primary platform. At peak production, Apple is manufacturing roughly 1 million iPhones per day.
For Apple to bring a whole new long-cycle-time process online for the next iPhone, […] they would need warehouses with thousands of machines already in situ, with thousands more in production.
Greg’s post is a fascinating read, which spells out several reasons why it’s highly unlikely Apple will be releasing a ceramic iPhone anytime soon.