I guess custodians are high risk when you don't have an easy way out: can't pull/send/withdraw more than $1k cash daily, or other similar restrictions. With the chaumian mints being described, one can swap his whole stack to a different mint in seconds. Thus bank runs are constant, not once in a generation. Thus, banks (mints) must behave accordingly. An important point is that self-custody is important for savings amounts, not so much for pocket money. On the other hand, a Californian's pocket money is savings (life-changing) for an African. When someone works for pennies and they manage after months (years?) of hard work to save 100$, it would suck to move it to self-sovereign on-chain wallet and pay 10% in fees due to mempool congestion. I guess there isn't a perfect solution (or I can't find it). But we're improving daily...