Comment 3 for bug 1690582

Thought about this some more. Since we can't really change onboard-autostart.desktop, we would handle "org.gnome.desktop.a11y.applications screen-keyboard-enabled" in the shell extension.

Basically, the extension would be installed and enabled at all times, but the indicator stays hidden until "screen-keyboard-enabled" is true. Onboard itself is then launched and killed by the extension as needed (or whatever else has to happen once embedding into the shell works).