Doubling or tripling the amount of data sent would be negligible over a wire, but an audio protocol won't be as snappy. Then there's the matter of trust/decryption. How are those keys being kept safe? What happens if I lose access?
Everything uses symmetric encryption, including asymmetric encryption. Using symmetric encryption doesn't mean you'd use the same key for every dishwasher, you'd obviously just pair the devices and generate a new key, like everything does nowadays. Also, my dishwasher doesn't use any sort of encryption, and it still leaks.
Doubling or tripling the amount of data sent would be negligible over a wire, but an audio protocol won't be as snappy. Then there's the matter of trust/decryption. How are those keys being kept safe? What happens if I lose access?