I haven't seen anything official about it, but I imagine it's been planned for some time. Sun/Oracle have explicitly warned against its use for a while. It seems less necessary when GC improvements in the last two releases have meant it's much easier to get great speed and latency with idiomatic and documented implementations. Further, what performance improvements are offered by Unsafe are obtained by breaking a variety of Java's guarantees, and I imagine that it is tiresome as an OpenJDK dev to hear about bugs "caused by the JVM" in libraries that depend on an unsupported undocumented API.

Just speculation, of course.