this dream of everyone demanding physical is something the gold bugs have wished for decades. it never comes close to happening.
most of the paper in the bitcoin system can never be redeemed for bitcoin, so there is no "calling it in". the millions of people around the world who hold the "physical bitcoin" etfs have NO right to call it in and ask for the underlying. so there is 0 risk to the custodians.
if they want to sell tons of paper bitcoin (well beyond the 21M cap), they can, as long as they hedge the price exposure in dollars as all they will ever owe to their customers is dollars.
