As mentioned in the beginning, it all depends on how many users request it. Also Vray and Corona are the two major players at present and while redshift may be the largest GPU renderer, I think if you look around the forums here, you won't see a lot of members talking about it and certainly not very many requesting a Forest Pack material library for it. As you can imagine, adding such to Forest Pack, would be a lot of work and unless you have a significant number of folk requesting such a library, it's not really a worthwhile venture... but since you seem to be the only one I have seen asking for this, I am not sure you will be seeing any progress on it in the near future.. I could be wrong but I imagine they have plenty of more important things to work on at the moment.. but good luck