I believe when you combine voxels with procedural generation you get something that goes well beyond the sum of these two parts. You can be very successful at any of these two in isolation, but it is when you mix them that you open up a whole set of possibilities. I came to this realization only recently.
I was watching a TV series the other night. Actors were filmed against a green screen and the whole fantasy environment was computer generated. I noticed something about the ruins in this place. The damage was clearly done by an artist's hand. Look at the red arrows:
The way bricks are broken (left arrow) reminds me more of careful chisel work than anything else. The rubble (right arrow) is carefully arranged and placed around the floor. Also we should see smaller fragments of rocks and dust.
While the artists were clearly talented, it seems they did not have the budget to create physically plausible damage by hand. The problem with the series environment was not that it was computer generated. It wasn't computer generated enough.
Consider physically-based rendering. It is used everywhere now, but there was a time when artists had to solve the illumination problem by hand. Computing photons is no different than computing rolling stones. You may call it procedural generation when it is about stones, and rendering when it is photons, but these are the same thing.
As we move forward, I see physically based generation becoming a thing. But there is a problem. Until now we have been too focused on rendering. Most virtual worlds (like game scenes) are described only as a surface. You cannot perform physically based generation in a world that is only a surface. We are missing the inner dimension.
Our world is 4D. This is not your usual "time is the fourth dimension" pickup line. The fourth dimension is the what, like when you ask what's inside a box. Rendering was focused mostly on where the what turns from air into solid, which is a 3D surface. While 3D is good enough for physically based rendering, we need 4D for a physically plausible world.
Is that bad that we are not 4D? In games this translates to static worlds, or scripted destruction at best. You may be holding the most powerful weapon in the universe but it won't make a dent on the floor. It shows everywhere as poor art, implausible placement of rocks, snow, debris and damage, also as lack of detail in much larger features like cities, castles and landscape.
If you want worlds that can be changed by its inhabitants, or if you want to generate content by simulation, you need to know your world as a volumetric entity. Voxels are a very simple way to achieve this.
Going 4D with your content is a bit of a problem. Many of the assets you may have could not work. Not every mesh defines a volume. Often, meshes have holes in them. They do not show because they are hidden by other parts of the object. These are not holes like the center of a doughnut. It is a cut in the mesh that makes it just a surface in 3D space, not a closed volume.
Take a look at the following asset:
The stem of this mushroom is not volumetric. It is missing the cap. This does not show because the top of the mushroom is sunk into the stem and this hole is completely hidden from sight. If you tried to voxelize this stem it would have unpredictable results. This hole is a singularity to the voxelization, it may produce all sorts of artifacts.
We have voxelization that can deal with this. If you voxelized the top and bottom together, the algorithm is robust enough to realize the hole is capped by other pieces. But we just got lucky in this case, the same does not apply to any open mesh.
Even if you get meshes that are closed and topologically correct, you are only describing a surface. What happens when you scratch the surface? If I cut the mushroom with a knife, it should reveal some sort of mushy, moist material. Where is this information coming from? Whoever is creating this asset has to put it there. The same applies to the bricks, rocks, plants, even living beings of your virtual world.
I think the have reached a turning point. Virtual worlds will remain static and very expensive to build unless we can make physically correct decisions about the objects in there. Either to destroy them or to enhance them, we need to know what they are made of, what is inside.