remdk I should have said unpublished rather than unwritten and have amended my post to reflect this.
There was definitely some mention of the adjacent seat blocking benefit at the time that Platinum was introduced, but from what I recall it was only for them. As a Platinum in waiting, I will have plenty of opportunities next year to see if there really is such a benefit.
The only advertised Y Class seating benefits for PC members are the Preferred Seats in the front of the economy cabin, and the upper deck of the 380's, though, in my experience, its usually well populated with non PC passengers, making it a benefit that only applies when the flight is under well under-subscribed.