Possible to daisy chain bluetooth speakers on auto-stereo?

I don't think it can be done due to security concerns. You wouldn't want someone else listening into your phone calls from another same Bluetooth device? Similar reasoning would prevent pairing same type of devices such as speakers. Though not an issue if using different hardware - speakers, and keyboard for instance.

However, my understanding is that Bluetooth devices use a unique ID, similar to MAC address. So may be possible if supported by current BT specs? I guess you'll have to just try and see if it works?