> Obviously nobody wants their dishwasher, washing machine, fridge, microwave, to put up messages, "is it okay to update now?"
No, I don't expect anyone to be asked to update. I expect it to work just like Chromecast devices do: It updates in the background while in operation and applies that update at the next reboot. If idle for long enough it'll reboot itself (usually in the middle of the night when no one is expected to use it).
Self-update mechanisms aren't rocket science. In fact, there's so many FREE options to choose from at this point you can just take your pick. Don't need to code anything on your own!