I don't think that we will see any more single-country-based expansions like an "England" expansion (Egypt being the big exception for understandable reasons). If there will be more big expansion sets they probably will be more "region"-based, however "region" can mean New England or the entire South Pacific with Australia. An European expansion would perhaps include most of continental europe and the British Isles, with cities being Paris, Berlin (far more important in the 1920ies than Vienna) and a third one and wilderness locations like Stonehenge. Since the Dreamlands 7 locations are at least possible on one board.
Edited by GBI