Its rare to see in sports and in golf, its not unique, but its rare. I would say its not really a thing to worry about. The thing is, his swing speed is insane with how smooth it looks. If you looked at Tiger woods, before he tore up his knee, it was violent. He would really snap that knee straight and fire those hips through hard. Rory, though his hips rotate fast, it doesn't look like they are moving that fast.
Also on a side note, that reverse is after impact, and has nothing to do with his impact, basically its his Obliques from the other side pulling his hips in reverse due to the speed he rotates them at, its basically a counter force. If you look at other golfer's kinetic chain, there hips are slowing down as well, Rory's just happen to go in reverse. Meaning every golfer has there opposite side pulling hard against that rotation to balance it out, Rory just happens to have his pull harder.
Also, i think Rory is in good hands with his work out instructor. I am sure that if he has any pain, that he will make the changes needed. Look at Bubba and Tiger now, they actually let there left foots rotate, and Tiger keeps his left knee more bent, allowing for the bigger muscles of the legs to take the force, instead of his knee. Rory can do this to if he needs to make sure he's not putting unwanted stress on his body. Really, the the areas he needs to worry about is the left knee. That area takes a ton of force in the golf swing. That will go before the hip does.