Self Custody is the GFY 
Discussion
Exchange for their ETFs? That’s why they call themselves non custodial exchange. The funds will be in the ETFs, not in EDX.
Blackrock ETF ~> Coinbase Custodian
EDX Markets ~> Paxos Custodian
Fidelity either buying Grayscale or launching their own ETF. Not sure details. 
we re mini banks ; under their system accounts are tokenized for better customer support