The elephant in the room is the IRS transfer certificate, Form 5173.
I believe IRS rule is that this certificate only applies to decedents who are non citizen and non resident.
But it appears that Schwab reqiures this form from the IRS in order to transfer your account to your heir after you've kick the bucket outside of US, even if you are a US citizen.
What about other brokerage firms such as Vanguard, Fidelity or Interactive Brokers?
May be I'll sell all my stocks, transfer my money into a Thai bank and make a Thai will.