We just came back from Vegas Saturday. We were curious about this too before our trip. I can say that at the Rio, they still had a priority line for Platinum at the buffet (It listed Platinum, Diamond and 7 Stars) but they closed the old separate entrance and moved all of the entrances down to the old main entrance of the buffet. The Rio buffet also closed off part of their buffet. The end to the far right of the buffet which had the salad, breads and other American style foods was closed and walled off. They moved the salads and breads to the far other end and we noticed they closed the Mongolian BBQ section. The Mexican food section was also shrunk down quite a bit. Lots of changes since we had been there last.
Also just an FYI for those interested - They also still had Platinum included in the VIP Hotel Check in area at the Rio as well.
We didn't visit any of the other Harrah's properties for meals so I can't speak to the other buffets.