Unfortunately that document doesn't quite answer my questions. It indicates that Cypress-proprietary SECI only works with Cypress Bluetooth devices. The document mentions the 3-wire coexistence, but in reference to Zigbee specifically. I'm not clear if there is a reason that BT/BLE is omitted.
Also, the document hints that 3-wire coexistence is only available on certain GPIOs, but only lists the pins for a single device (CYW4343W). It does not indicate which GPIOs are available for this feature on the CYW43907.