I think for C4d, can be easy, beacuase in C4d from the R12, can use Python, and how I say in another post, the exporter have to be similar than Blender. Litghwave I don´t rebenber now if supports python.
Only for advice, for 3DS MAX have a very good exporter from the friend Vladimir, I use exahustively and works, very, very good.
In other part, I think the importer are very important, but I like if it´s possible have a little set of predefined Shader, or materials, for have shine, specular, and well ... will be great if the normal map, works in all platforms.