neilt notes this eWeek article where sources indicate Quark 6 will be Mac OS X native (Carbon) and is likely due in early 2003:
Sources predicted that Mac and Windows versions of XPress 6.0 will debut in early 2003, perhaps in time for January's Macworld Expo/San Francisco. In addition to Carbon support, the upgrade will feature PostScript 3 support and a new XML engine to replace the company's current Avenue.quark XML-conversion application.