Andrew says it's coming. I suspect he is wanting to get the voxel>surface feature working fully first. The Move brush will use the surface mode.
I personally would like to see all brushes work on voxels. I'm not too keen on the idea of switching modes. But I can imagine that creating new brushes for voxels will be quite time consuming. But early days yet.. I've got faith in Andrew. Whatever he does, he'll do it for a good reason