The 4x4 limit just seems really arbitrary. Even if the devs don't ever want to consider adding depth to the zoning area, I really can't see why longer lot sizes (along the road, think 4x5, 4x6, etc.) aren't a possibility, as they would work entirely within the game's existing mechanics. Right now, all the zoned high-rises have to fit in a 4x4 area, really limiting their shape (skinny and square-ish). At least the possibility of more elongated lots would allow for a greater variety of building shapes.