This is quite old thread, but my post propably isn't worth starting a new one.
I recently replaced my T5.1 LWB 3-piece propshaft with a T6 2-piece propshaft(this was also available in T5.1 after 2/2014) and is interchangeable with each other. All of the cv joints can be fit in both style shafts.
I had to replace the rear cv joint, because the old one was stuck quite badly. VW or aftermarket brands don't offer a replacement joint, but I found Land Rover Freelander 2 uses similar enough joint in the propshaft and can be used as a replacement one.