This is an amazing project. I avoided the Personal Assistants for the exact reason you mention...someone looking at the data. There is no way to trust Microsoft, Google, or Amazon.
I wonder what this company will do with the data. Yes cloud has to be out but even on one's device, it will still be vulnerable. Great Hunt though.
Check out Enigma Protocol. They are working with Intel to make it possible for computers to process information without actually giving the computers access to said information. The privacy itself isn't battle tested. But it's a real project that is being worked on.