Aside from performance, the biggest issue with making WCU larger is the terrain size, or rather terrain resolution. Every other official level uses heightmaps that are at 1 pixel per 1 meter resolution, with 4096x4096 being the largest possible heightmap. But because WCU needs the steeply inclined roads of Belasco to be drivable with such sharp grade changes, it uses 2 pixels per meter. So while Italy is spatially 4x larger than WCU, both maps are running the terrain system at its limits. If the devs were interested in pushing the terrain system to accept larger heightmaps, a boost in WCU's size might be on the table, but that's a big development, and some of the larger mod maps have demonstrated that going bigger has stability problems with nearly every tool and feature. It would also probably require a partial rework of even the extant parts of the map, so my money's on it being outside the scope of a ~5 month development cycle.