POWER9 and Hardware Assisted Garbage Collection

[amock]

Does anyone know what happened to the Hardware Assisted Garbage Collection feature that was supposed to be in the POWER9 CPUs?  It is in the v3.0 spec, but  not v3.0B so the documentation was removed, but I can't find any mention of the removal.  It's also mentioned in the news from around the time of its release.  I'm guessing that it just didn't make it in to the final silicon for some reason, but I'd love to know if there was ever a reason given.