And since the pitch is “we want anonymous international depositors to open and close accounts with you,” with extra steps added, no bank will agree.
But there is the need for everyone to trust the ETF manager. Authorised participants (APs) must trust they can redeem ETF units for a basket of the underlying shares and vice versa. Other market participants, in turn, must trust that process to manage tracking risk.
ETF managers earn that trust by contractually guaranteeing APs' creation/redemption rights, being regularly audited like normal companies, being regulated like securities companies, and having their holdings vouched for by other market participants, e.g. banks, clearing and settlement services, et cetera. Literally none of the preceding apply to Bitfinex nor Tether.
More broadly, a structure like Tether is inherently incompatible with anti-money laundering. No jurisdiction will let a bank say "these $2 billion are held by unknown beneficial owners." If we wanted that, we'd just re-authorise numbered, i.e. anonymous, bank accounts.
[1] https://www.bankdirector.com/index.php/magazine/archives/2nd...