Once you get into materials and fabrication, having a finished example to examine is rarely going to lead to a big win. If the secret sauce is in the fabrication (HOW do you make a single crystal blade? HOW do you inflate corrugated titanium? HOW do get this type of grain structure with this nickel-iron-manganese mix? HOW do you get a laser weld in this impossible again?), then a single example isn't -THAT- useful.
Reversing engineering a modern turbofan(remember, the basic principles of turbofans are well known) is more akin to reverse engineering Intel's fab process by peaking at a finished i7 (with AFM and electron microscopes) than reverse engineering say... a sensor fusion module once you get the assembly code.
Which is why the technology transfer associated with the engine deal is a big deal. It should (I mean, its possible that the terms are all fucked up) give the Chinese an oppourtunity to learn all of these hows and whys (albeit for a slightly dated design, but still a relatively modern one).