Please add more shapes to the flattening tool, like squares not just spheres. Please add a way to flatten vertically, like making walls, instead of just horizontally. Please add a way to mark the terrain, like with virtual blocks of some kind, like a block structure of some sort that adds marks to the terrain, so you would flatten the terrain inside it, either with the tool, or with a flatten bot similar to the auto miner.
Great ideas. Especially the bit about marking the terrain. We need some form of land surveying or laying down a grid to guide flattening operations.
The primary missing tool in the landscaping is "smoothing" - the ability to pass the tool over bumpy or jagged land and smooth it out - not flatten it, just make it smooth (and if that results in a slope, it's probably what the player wanted).