Writing a RenderMan interface that not only writes RIB files but also takes care of full shader translation and texture map conversion is not easy: There are too many things that each renderer does in it's very own way and that does not translate to the other. In my opinion, eF should rather spend the development time on improving FireFly itself than implementing a 3rd party renderer interface that <1% of its user base are interested in. Writing a universal interface is not easy: Each renderer I have seen so far has its own format for texture and shadow maps and has different ways of how it deals with raytracing in the RIB file. Shaders are also different, I've had a lot of .sl files that one renderer would compile and the other wouldn't. After all, the pricing of commercial RenderMan plugins suggests that it is not cheap to provide full solid support: Animal Logic's MaxMan costs USD 990,00, Maxon's RenderMan support for C4D is only available with their very costly Production bundle.