This is probably the most realistic rug I've seen in 3d - I'm happy to see other examples, but to this point I have not. I purchased the project files and studied the implementation quite a bit, and frankly I'm having a hard time replicating the implementation in Ornatrix - not to say it isn't possible or easy.
My main observation is that the 'hair' (threads) are actually little squares, not thin strands as you normally see with a hair / fur system. The shader for the hair / fur is actually just a basic white hair from the Corona Material Library, but somehow the lighting in the scene really drives home the semi-translucent quality of the top layer of carpet.
Apart from the shader, I think the effect that really sells the look of the rug is:
1. subtle displacement to simulate folds
2. manually combing the groom to simulate foot traffic
3. the (sort of) beaded rows of pile that render as small tufts - I don't totally understand how the associated bitmaps are driving this effect.
I'm wondering how generalizable the implementation is to simulate other carpet / rug types.