I would love to see an option (similar to commit-confirm for config changes) that works for system images, something like:
"set system image default-boot {1} confirm {10} rollback {2}"

Basically set the default boot to image 1, reboot, if not confirmed in 10 mins, set default image back to image 2 and reboot again. This would be helpful when upgrading remote systems where a breaking change is possible.