The scenery gap between countries is the reason I do whole continents. With smart exclusions it should also work, as there are only exclusions set where facades are, but I have a prework algorithm to speed up the generation of OSM sceneries also for huge data files. Also a problem with multipolygons was, if a building or forest is over the border line of two tiles, you have to split up into two separate objects. And sometimes we had to correct the faulty points of an inner/outer ring or to decrease the number of points. There were many many things we worked on with the MultiOSM2XP tool... At the beginning I thought, well, that's easy, two days of work for Daikan, than we needed several weeks...