for the functionality to import grouped products, the new libraries techdivision/import-product-grouped and techdivision/import-product-grouped-ee has been implemented. Additional major customizations in the library techdivision/import-product-link has been necessary.
The changes also affects the configuration for the CE, as well as for the EE. For the EE, checkout the diff of PR48 to see the necessary configuration changes. For the CE, have a look at PR134 and PR135.