Remind repo owner to upgrade metadata on SFDC version change
Your blog post https://gearset.com/blog/mdapi-versioning-and-version-control says it all under the paragraph labeled "Upgradingyour repository's metadata"
But there's no real reminder to tell the team that this is a meritorious idea. My suggestion is that for the first 30 days after PROD is updated, you could display (in color) some alert (or maybe introduce a messages feature) wherein you tell the team that the repo's package.xml is out of date (version wise) with PROD version and provide pointers on how to upgrade, including nuances like Flows (v44).
It is too easy to get lazy and leave the repo metadata out of date causing issues with standard objects during in-the-heat-of-the-moment-comparison/deploys.