Voxel Plugin supports approximated smooth blends. This solution uses the standard one-material-per-pixel shading pipeline, but dithers the material selection to give transition areas a smooth appearance.

WARNING

This solution relies on TAA/TSR to resolve the dither effect. Without this, a 'speckle' pattern will be visible.

The smoothness of blends between different materials is controlled by the Blend Smoothness value in Voxel Surface Type assets. If a surface type has a blend smoothness of 0, it will always have hard edges, regardless of the blend smoothness of the other surface types it's blending with.

To mimic the old 'pure' Smooth Blends without height blending, feed a constant value of 0.5 into your material's displacement pin. If you see any sort of banding (especially likely with no or low-frequency displacement), enable the Dither Noise Texture property in the MegaMaterial. Without this, there are only five possible blend intensities. The added noise can hugely reduce how visible those bands are.