How would that help? It appears to provide a subset of Home Assistant's functionality.

I thought it provides simple alternative (as asked) with voice commands. But when reading the details the voice processing is not offline (as asked).

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Note that in the 0.8 gateway release, browser-based voice commands are processed using Google’s voice assistant API, so the audio strings are processed in the cloud. The speech-to-text result is passed back to your gateway. If you instead type a command into the text field of the smart assistant screen, those commands are processed locally and do not require a connection to the Internet.

https://iot.mozilla.org/docs/gateway-user-guide.html

EDIT: But hopefully they will move to something like offline Common Voice in some future release.

Home Assistant's Almond/Ada integration does the same thing (without sending anything to Google)