Organizers and drivers from France, Scandinavia or the British isles have rarely been interested in ERC, especially when one considers they're all big "rally nations". So it's not always easy to go to the places currently left untouched by the calendar.
To me an event in Belgium, Germany, Austria or Switzerland would be nice to have, but for the rest I don't see big problems in the calendar. Barum is definitely central Europe, not East. Both the Hungarian and the Polish rallies are central-east Europe, while Liepaja is not far from Scandinavia.