I’ve added an issue on GitHub. Bear in mind that, unlike Classic’s Geolocation plugin, the Mapping module allows more than one marker per item, which complicates our assumptions about what should go into the popup. Item owners can already modify the individual marker’s label and thumbnail, so we have to consider that as we move forward. For now, you can fully customize the marker’s popup content in Mapping/view/common/block-layout/mapping-block.phtml