Sure. Those platforms are highly dependent on centralized liquidity providers that represent a single point of failure.

Swan lost Texas recently afaik since Prime Trust (temporarily) lost money transmitter licenses there.

If I were a regulator trying to choke the market, I would go after the businesses that enable MTL "pass through" where companies can build a widget on top of the brokerage without MTL.

Check out article I wrote. Liquidity fragility to me is no different from overall fragility since it means single point of failure for falling out of compliance. Some brokerages as a service might be more robust than others, but all of it is somewhat opaque.