I don't think it is common to have a Google Document for just a note, or even a collection of notes (it is not clear from the example videos if your thing will replace the entire doc with the text said or if it will add it to the bottom of the doc).

This is something that fits better into other apps that have small collections of notes as their primary data type.

That's great, but not very useful. Maybe it would work better with smaller documents and simpler tasks, like Trello, for example (create a card, update a card description, set a due date on a card and so on), or other task management platforms.

I don't have Alexa and talking to a computer is still too bizarre for me, but sometimes I wish I could take notes while driving.