This isn't very effective because a longer, more specific prefix wins. It
would immediately inflate the route table to its maximum size if the registries
announced every possible delegation. It is similar to the problem with people
hijacking addresses. Unless you tie it to filters which ignore prefix
announcements longer than the "authorized" allocation size. Which brings us
back to the start of this thread.
If AS1239 and others contributed and used something like the IRR to filter
announcements, the problem is simplier.