There will be options to help reduce the face-count. You can disable caves and enable solid ground, which will fill in those empty spaces. Even if you offset the terrain height to a scale other than 1, there will an option to fill in gaps between displaced bricks resting on the ground using 4x4F plates. You can also set the "terrain height offset" to a lower number, which will reduce the height of the caves and thus the number of bricks/faces rendered. Hopefully that won't be too much of an issue.
Poll