Was there any progress on this topic in he last months?
I would be very interested in how you got your implementation working. Generally I would like to achieve something similar:
I implemented a simple Raytracer for volumes with arbitrary gradients (to render gradient lenses/eyes/fluids of different density, gravitational effects, etc), which can run on the cpu but also supports cuda. It would be very nice to get that running inside blender, but I have no experience with the cycles-code. So I would appreciate any help or getting insight into your code.