So I have created a patch to cull off objects based off of distance from camera. Most of my code has been based off the camera culling part.
How is this useful? well, we have some production scenes at the moment, but we can't use camera culling on a lot of objects due to reflections... with camera culling & distance culling combined, we have a minimum distance that the objects are visible in (which is defined in the simplify panel).
It is also useful for small objects to be culled off when far from camera as well.
If there are any questions just let me know and I will try to address them as soon as possible. I apologize in advance if my code isn't up to scratch, I am quite new to the cycles kernel.