I saw @iquilezles sdFbm article (iquilezles.org/www/articles/f…) and tried it in blender.
5 octaves of noise, 16 raymarching steps. That's all opengl can handle before hitting uniform limits with nodes.
As you can imagine, lots of nodes :D
The node editor lags to death, but viewport is nice and fast still (since unrolled loops run about the same in the end on the GPU side)
Note there's no drivers in the shader, as that *wouldn't* run anywhere near as fast!
Here's an overview of the nodes, with a little bit of annotation to show what each chunk of nodes is doing