[_red]

>dual-root-type setup where they update the inactive root, boot into it,

Fedora-IoT effectively does this with rpm-ostree + greenboot.

Greenboot specifies a series of directories under /etc that organizes your custom scripts (scripts that must not fail, scripts that may fail, scripts to run on success, scripts to run after previous failed, etc) then it marks your current ostree as either being active or auto-rollsback into previous.