This is one of the best exploit presentations I've seen, and that's without considering the twist at the end. Humbling and inspiring. Thank you!

Did you look into whether the spoofed device can also be "upgraded" to be used as an HID device, like a mouse or keyboard? That upgrade would be several CVEs against the OS vendors.

That would make the attacks potentially silent, since the attacked could simulate keypresses to dismiss notifications, or can at least keep the target unable to respond by spamming home/back or pressing power and simulating a swipe to shutdown.

I believe this would in any case require repairing and the new functionality would be visible in the pairing UI? I would be surprised if a device once paired as a headset can suddenly start acting like a keyboard if it feels like it.

EDIT: Covered in the talk at 33min. No keyboard but the Hands-Free Profile would allow you to place calls and interact with a voice assistant if one is enabled.

You can't change the device class.

It would be an vulnerability on the host stack to accept that.