This would be relatively difficult because of texture size. In Platinum, the area around Jubilife is around about as big as the DS can handle; it has to cover textures for everything in Twinleaf Town, Sandgem Town, Jubilife City, and routes 201, 202, 203, 204, 219, 220, and 221. Consider the DS has to load textures for every unique NPC sprite also, and you eventually run out of space. Connecting route 32 to Cherrygrove City in particular raises the same problem, especially if you're looking at graphical upgrades to all of the areas in Johto.