All that I am speaking of is mesh imported in and out of Blender but it has special needs and details that are needed for understanding and display. A Terrain.raw file is a 256x256 face mesh that is uploaded to OSGrids and provides the "Ground" that all the rest is built on. OSGrid then textures it in its own way that would be nice to at least simulate in showing and discussing. Also in the Raw file itself is data about water levels and mountain heights that would not translate in the Blend file even though the data would be there.
Sculpted prims are a different kettle of fish. They were invented a few years back (10?) when somebody realized that since colors were translated as three numbers, those numbers could be represented as X,Y,Z and be 3d points, but again have special needs as they are passed as 2d images and translated to 3d, very much as iff you had a stretchy paper and made origami. In order to limit computer use the size was fixed at 1024 faces and much of the work done by textures that are also made in Blender.
All of which could be uploaded as a blend file (as about any 3d object could) but would not make much sense in that format, as different from any other small mesh, and would include the 2d image as a "texture" as well as the actual texture used to color the object.
I think it would be good if such objects had their own category due to their specialized nature (even if Raw files and sculpted prims were in that same category.