Both sun-java3d-bin and blackdown-java3d-bin exists but there's no java3d-virtual like there's an virtual/jdk for blackdown-jdk and sun-jdk.
I agree, the ebuild http://bugs.gentoo.org/show_bug.cgi?id=112212 is dependant on blackdown.
http://svn.gentooexperimental.org/svn/java/axxo-overlay/ There should be initial support for virtuals in java-config. After we get this moved to official, we can think about implementing a virtual for this. Just be patient.
There's no blackdown-java3d in tree anymore so I guess this bug became moot, unless there are other java3d implementations in which case reopen