Add calculated field for mapping to destinations

Currently, if you share an audience to e.g. Facebook Custom Audience, you can do only a 1:1 mapping of your xdm schema field. As some destinations have specific requirements, it would be great to have like a calculated field as an option (same as in datastream mapping). One example would be to lowercase your xdm schema fields, as e.g. Facebook Custom Audience needs firstname / lastname in lowercase. As of now, I have to ingest an additional field with lowercase firstname / lastname to make it happen (or do some query service magic). I guess some simple adjustments / transformations of your current xdm schema fields would be very helpful.