Anything ‘virtual’ , virtual-textures, RVT, etc is ‘chunked’ or tiled so that the engine tries to work with what it only needs, getting at a subset of a texture or the like.
My understanding is that this type of tech is distinct from anything else, it only applies to the texturing step. Nanite uses triangle-clustering and some kind of pre-computed visibility to assist the rendering step in culling to just-about what you need to see vs the raster, layering process.
The VT’s would come into play when the engine actually draws whatever, nanite helps in determining what to draw.
What you are talking about, combining stuff into a single unit is essentially texture-atlasing. This works on it’s on level to provide benefits to resources and complexity, but doesn’t really do anything in terms of culling or displaying triangles. Yes, I would think that atlasing would still give you a benefit but not at the part of the engine you stated as atlasing works to optimize texture-paths not mesh-paths.