In areas where I need the actual vertex material ID I round it in the material so it ends up being the value of the closest vertex, haven’t had any real issues with it so far. The side of it is way behind my cubical volume implementation though so I don’t have any pretty images of MC. I got really sidetracked adding Voroni fracturing, and physics particles / gravity to the volume and let the lag behind a bit (it breaks with a lot of the new features, haven’t gone back to fix it yet). I did things a little differently with the texturing but I can’t remember off the top of my head what it was.
Normal generation is DDX / DDY and I have a post in this thread somewhere where I have the node layout for it (also an example of combining the result with material normal maps). This also means that I don’t need to duplicate vertices across triangles where they meet since the vertices don’t need normals/uv maps at all this way, texturing is done with triplaner mapping (as you are using).