John (C), just out of curiosity, is there a good count of how many of these resources exist (i.e. legacy resources without an LRSA?).  If you can easily say an aggregate number I'm curious.

In terms of IPv4 address space not under contract, less and less each year…  About 42% of the ARIN registry space is legacy resources not under contract, and this has been steadily dropping.   It was obviously 100% at ARIN’s formation, and presently slope is about -3% per year.

In terms of organization count -  

Is there a count of how many of these are present in the DFZ, or that are being announced by larger netblocks, or which do not show in the BGP table at all?

Excellent question, and the answer is unknown.  The fact that such a statistic is not easy to derive from public information is something that was recently brought to my attention and we will work to fix shortly.

Given, this is a list of potentially-hijackable address blocks, so I don't know that such a thing should be posted publicly, but I could see research being done with the full set under a confidentiality agreement.  (If such a thing has been done, please point me at it).

I have not seen such work done. 

This feels like an interesting research presentation/lightning talk/something to me, relevant in the world where we're talking about declawing third party registries.

We do provide bona fide researchers bulk access to registry data <https://www.arin.net/reference/research/bulkwhois/> (and could provide additional instrumentation if necessary for such a research activity.)   

FYI,

/John