When https://issues.redhat.com//browse/CORS-3652 is implemented, there will be a new stream available in the rhcos.json/coreos-bootimages configmap. All new installs in 4.20+ will be using this stream for boot images. On the MCO side, we can use this new stream to

• Transition older MachineSets(4.12 to 4.20) who are using image galleries to unpaid marketplace images
• Transition older MachineSets(<4.12) who are using managed images to unpaid marketplace images
• Perform updates to Machinesets that use unpaid marketplace images: this includes new installs 4.20+ and ARO. 

More context in: https://issues.redhat.com/browse/MCO-1672?focusedId=27560148&page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel#comment-27560148