We will see what happens for ZBrush 3.5 and 4.0
I dont know the road map of it.

And you can believe me: I am excited about voxel sculpting. I am a licensee of the C4 engine also and we can sculpt the terrain with voxels there. The whole 3d-space around a terrain is divided into a big data matrix and can store information of the terrain (collision data, geometry, texture data and position of the triplanar mapping). So you can even carve a cave into the terrain or bild bridges between 2 hills.
This is not much different than these modeling tools work. I believe this will be the future of modeling and rendering.

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