Actually, alternative app stores can make use of that as well. The installer app needs to be installed as a system app with proper permissions, and it will them

Actually, alternative app stores can make use of that as well. The installer app needs to be installed as a system app with proper permissions, and it will them be able to background install apps on demand just like Google play does. The F-Droid Privileged Extension[0] does just that. While you need to be rooted to add/register such apps, that's not a problem for device manufacturers. [0] https://gitlab.com/fdroid/privileged-extension/ https://gitlab.com/fdroid/privileged-extension/