There has never been a requirement to announce address blocks, private use of globally unique addressing is sufficient reason for an allocation in my opinion.  Addresses don’t have to be announced to be in use.

However, as a matter of basic principle, I think there should be a simple policy statement that completely unused address blocks should be returned to the original allocating RIR, especially if there are no plans to use the address blocks in the foreseeable future, but I don’t believe there needs to be any organized enforcement actions of this basic principle for IPv6 at this time, maybe several decades in the future some level of enforcement could become necessary and prudent. Nevertheless, having this basic principle in policy for several decades before it is needed would prevent any arguments to the contrary, when or if the time for such enforcement ever comes.

Thanks