3dm files would be great for layers and other attributes, but there is one downside of 3dm for meshes - they don't support n-gons, only tris and quads. I think this may change for Rhino V5 or V6, but if n-gons is a big selling point of MoI's mesher, 3dm is not the ideal format.

Then again, if you're importing back into Rhino for rendering, the obj would be converted back to quads and tris anyway, so it would probably work for Micha's workflow.

Our T-Meshes are sort of an overlay onto Rhino's meshes, adding support for n-gons, T-Points, and knot vectors. But if you render a T-Mesh, or load one of our T-Meshes in Rhino without the T-Splines plugin, it'll just be quads and tris.