Is it possible to import metadata for Media with CSV Import module ?
That’s unlikely. Since media are always attached to items, there’s not a good way to map metadata about media from a CSV file – the structure doesn’t allow that kind of nesting.
Is it possible to import metadata for Item sets with CSV Import module ?
That seems like a reasonable possibility. Just as CSVImport lets you specify whether you are importing Items vs Users, it seems straightforward to do an import of ItemSets.
CSVImport includes some of the features from CSVImport Plus (like working with Sideload). Dunno whether the best path is to try include the specific functionality into CSVImport, or have people fork as needed.