b) if the FBI is successful in compelling Apple to develop a backdoor for the iPhone there's nothing stopping them from compelling Amazon to do the same with Echo.
No backdoor needed if they information is sent to Amazon. All that is needed is a court order for Amazon to hand it over.
Sure, but all you'd get are commands you give Alexa ("Alexa, turn off the lights", "Alexa, what's the weather today"), which I suppose could be interesting to law enforcement, but certainly not as interesting as the "full-take" of an always-on wiretap.
I'm suggesting in order for the FBI to use Echo (or any other internet connected device that has a microphone) as a wiretap, the FBI could try to compel the manufacturer to write, sign, and push an update that causes the device to transmit audio to the FBI at any point.
That would have seemed a little far fetched in the past, but the current FBI/Apple situation could set a precedent.
No backdoor needed if they information is sent to Amazon. All that is needed is a court order for Amazon to hand it over.