Earlier quoted context omitted.
An appliance could just have blutooth so it can connect to an app on your phone. With the machine not having a direct internet connection, the app can collect diagnostics, metrics and do software updates. Require you to press a button in the machine to pair it to your phone. 99% of the functionality with 0 annoyance and ~0 security/privacy risks.
Yes! I've been thinking about bluetooth and a standard protocol and generic app. You'd get basic gui functionality for any compliant device, showing whatever device specific stuff the manufacturer wants. Kinda of like a bluetooth X-terminal, but way way simpler. Think tkinter over bluetooth, probably sans canvas. A bunch of people will say to just use wifi, make the device a Hotspot, and use your web browser. That's…
A long time ago I developed a project called "Handbag[0] for Android"[1] based around a similar concept--it targeted the short-lived "Android Open Accessory Protocol" initially over USB & later also over network/WiFi.
(My project notes from the time mentioned a long-term goal of also supporting Bluetooth but that never eventuated...)
Handbag made use of a "generic" Android app for UI display/interaction and an Arduino library that communicated with the app over a binary protocol.
The app would display various UI widgets such as labels/progress bars to display feedback from the accessory and text inputs/buttons to accept input forwarded to the accessory.
While the project did not take the world by storm, I was reminded when digging up these links that at least one person called the concept genius[2]. :)
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[0] Because it let you "accessorize your Android phone or tablet". :D
[1] https://web.archive.org/web/20130205135845/http://handbagdev...
[2] https://www.doctormonk.com/2011/11/handbag-android-and-ardui...