Just my 2 cents,
Iges, step, and parasolid formats are for parametric models. These formats are used to represent Nurbs and offer you nothing as a format for polygons. Make a complex shaped solid with a loft. You have created a BREP surface topology. B-Rep solids are Euler topological boundaries). This could also be described as manifold surface in a Reimann space. This is a parameter driven model, hence, parametric.
To better understand a parameter model. Make a circle and extrude it. You have a primitive function driven by two parameters u and v. r(u,v)=(acos(u), a sin(u), v) where v is your extrusion length. Parametric Feature based modeling uses primitive geometry like a spheres or torus, NURBS curves and surfaces, it uses parent/child design trees (much like LISP), and is full of Geometric relations, equations, and dimensioning. NURBS are controlled by knot vectors. Curves can establish Positional Continuity, Tangential Continuity, and Curvature Continuity; (C0, C1,C2) respectively. G0, G1, and G2 continuity is positional, tangential, and continuity respectfully, can be established in surfaces. Solidworks, ProE, Catia, Unigraphics, Rhino, Maya, 3Ds, …etc is built for this stuff. Blender has the ability to use Nurbs primatives and you can model them like clay. I would actually use this program if you could output the NURBS. Solid Modeling is actually just a set of feature based surface creation macros which form closed solids.
Polygons formats are just points. What you are actually viewing on your display when working with NURBS is polygons. Your graphics card takes this NURBS geometry and tessellates it. Your display is showing you rendered triangles of the solid or surface body. This geometry can be tessalated into polygons and saved into the thousands of formats out there as well. The parametric packages were not built for large polygon counts, it treats them as bilinear nurbs patches.
People will often say, well, if I convert the file to this format, and program x will read this format then I have accomplished my goal. Remember that even though polygons can be stored in iges format that doesn’t mean that these parametric packages will handle these large polygon counts (they all read .stl already) and most choke on large polygon counts and you can’t do anything with them other than use the verticies for reference geometry. The goal should be to get the NURBS in and out.
Everyone uses polygons for graphics (open GL, direct x). All display is triangles, then gridded as pixels. Triangles can be decimated to reduce data size without noticeable loss in detail. Triangle counts can be reduced and shaders can display them as smooth on your display (New DirectX 10 for Vista, Holy Cow). You can Add texture to them and you have all the geometry for graphics and shaders are applied in the graphics card pipe. TINs are used in GIS data. FEA uses triangle meshes. rapid prototyping, even CAM and CNC contollers is interpolating across these splines or surfaces to a tolerance to create linear moves from point to point. There are hundreds of uses. Tessellation of NURBS geometry can be done in a number of methods. Quad tree methods are commonly used. Point clouds can be tessellated with Delaney triangulation and Voronoi diagram methods.
To go from polys to nurbs you need advanced surfacing tools to develop curve networks and algorithms to curve fit the polys. I have tested all the auto surfacing tools in all the reverse engineering packages (best: Raindrop Geomagic, Rapid Form). None of them are perfect.
If blender was able to build off of the existing NURBS structure, (more than just Nurbana integration), and focus on using Nurbs geometry with a parametric approach, and then give the ability to output these nurbs, and I guess you’d want the ability to import them, it would be a valuable tool for Industrial design and advanced surfacing.
I see blender as a great polygon tool with limited NURBS and Parametric Functionality. If you are going to make blender a full on nurbs modeler with imort and export then go for it. I might actually use it then. Good luck.
RFUS