I haven't done any graphics programming in years, but I thought you'd want to keep the number of draw calls down, do you need to cluster these triangles into fewer draw calls?
GPUs draw can draw 10,000's of vertices per draw call, whether they are connected together into logical objects or are "triangle soup" like this. There is some benefit to having triangles connected together so they can "share" a vertex, but not as much as you might think. Since GPUs are massively parallel, it does not matter much where on the screen or where in the buffer your data is.
Is there any work being done to optimize a volumetric representation of scenes and from that create a set of surfaces with realistic looking shaders or similar?
This is basically where the field was going until nerfs and splats. But then nerfs and splats were such HUGE steps in fidelity, it inspired a ton of new research towards it, and I think rightfully so! Truth is that reality is really messy, so trying to reconstruct logically separated meshes for everything you see is a very hard way to try to recreate reality. Nerfs and splats recreate reality much easier.