Similar to T120452, we need to enable GeoJson storage on Commons.
The data will be stored as Data:<anything>.geojson (extension name bikeshedding is welcome: .map, .karta, ...). Data will be stored as geojson, but it will not contain location/zoom/map size. Each wiki will be able to reference it via the <mapframe> or <maplink> tags.
This data should not be too big (as it gets downloaded to the client). so the 2MB limit should be sufficient. For larger datasets, we will need to implement Maps (Kartotherian) support, just like we did for the OSM data.