Sounds right to me, that's pretty much how storagecraft do it, boot to login prompt, take screenshot and email it.
We've used StorageCraft for backup for years, this was one of the original winning features for us.
https://support.arcserve.com/s/topic/0TO36000000Ln5gGAC/advanced-verification?language=en_US
During a live vlog with @lawrencesystems the conversation came up with regards to automatic backup verification. For example Veeam, Storagecraft, etc. allow for booting up backups and taking screenshots (usually with network disabled) to ensure backups actually boot.
It was an interesting topic to see if this is something that would beneficial to XO, leaving this here as per @olivierlambert to open up the discussion.