There is a command to “pair” which will let you temporarily pair a Bluetooth device with echo. At that point echo becomes a Bluetooth speaker for the other device. So it works the same way as any other Bluetooth speaker. You control sound selection and volume from the other device, not the echo. You can’t do any other echo commands, I think, during that time. You have to pair before you go back to using echo as echo.
So it’s the foundation for something, but not something most people will use in its current state.