What nobody ever wants to discuss when talking about Sparse Voxel Octrees is animation.
You can’t animate SVOs very well, bone rigging is a nightmare. Not to mention collision hulls. So you’d still be using polygonal rendering for all skeletally-driven objects, and you’d need to keep polygon data on-hand for all physics/queries/etc.
So even if SVOs can work for making cobblestones look super-good up close without chewing up all your FPS and disk apace (and NVIDIA has a tech demo and whitepaper on this that seems interesting), all of the workflows and pipelines will still require old-school polygon-based meshing for most of the critical objects and assets in the game.
And having to simultaneously render both would further compound the processing expense and complicate the workflow… And it’s sort of like, is really detailed cobblestones all that worth it?