I have personally stopped using Firefly, making materials for it is a pain, just try to load some of Posers default materials setups, its insane to say the least. I don't think you will find any render engine out there which requires such a setup to make a material, and then it even look wrong :D, I doubt even in the movie industry they would use something like that. To me its the result of a render engine which is outdated with very little future. Even if you manage to make a decent material, in most cases it wont work correctly in different lighting which is a huge benefit with PBR materials as its physical accurate and also there are simply things in Firefly that you cant do, because its not part of the engine.

My guess is that a lot of people are very used to Firefly and therefore most of their content have Firefly materials, which doesn't always render well in Superfly, meaning you might experience noise, fireflies, color issues and also that its not as simple to convert the texture maps to Superfly. For instant you could take Superfly textures and plug them directly into blender, daz3d or any other PBR render out there and they will work. But there is no easy way to transfer a lot of math functions, reflection and refraction shaders and expect good results. No one is forced to render in Poser, blender is free and so is Daz, so even if you don't like working in those programs for whatever reason. you would only have to learn how to render in them.
PBR I think have a vey bright future ahead of it, Because computers get faster and faster, which does little for the quality of Firefly renders, except them being rendered faster, but so will PBR, but with a lot greater quality and it probably wont be to long before its almost real time rendering in the viewport (At least I hope, think :D).

"At GDC 2013, Epic Games released the Unreal Engine 4 "Infiltrator" demo, running 100% in-engine in real time, showing off UE4's high-end rendering features as well as the latest tools."

"Infiltrator" demo

I don't know how many vendors include PBR materials in their products, but I think its sad if people in the community refuse to support them due to that, because its not helping moving things forward. Most vendors work with other programs as well and are most likely somewhat up to date with what is going on besides in Poser and Daz3d. It would be a lot better if the community started moving towards PBR and demanding that, as it would make products they invest in last a hell lot longer, as it doesn't seems that the general setup of PBR materials are changing anytime soon, if ever.

But I fully understand the frustration that people might have with Superfly or Iray, because renders can take a long time, there might be varies issues like noise and so forth. My best advice is to make sure that objects used in the scene are actually PBR friendly, because wrong ones can cause problems and also a lot of issues can be fixed if you simply render your image larger (10-100%) than what you need and then resize it.