I still have one feather pillow from about ten years ago. It's still a pillow, but it's gotten lumpy, less full, and it's really only still around because of a strange nostalgia. It got to the point where it slept poorly at about a year. To be fair, it wasn't the "best" possible.
Buckwheat, I got a little longer before it lost enough filling to break down that it wasn't viable, about two years before I was just done with it being progressively flatter.