More on that from the source itself:

WHY IS FINRA 4320 SO EXCITING TO THE SECURITIES LAWYERS AND THE CORPORATIONS THAT HAVE SURVVIVED THESE NSS ATTACKS?

1) It finally addresses abusive naked short selling in non-reporting issuers. Up until now the regulators and SROs have found that the investors in development stage corporations somehow did not deserve the provision of investor protection.
2) Even though it is entitled “short sale delivery requirements” it covers the failures to deliver (FTDs) involved with intentionally mislabeled “long sales”. One way to bypass the newer short selling rules is to illegal mislabel your short sale as a “long sale” and just voluntarily fail to deliver the shares.
3) It affects FTDs held in “ex-clearing” because all (approximately 1,000) clearing firms that are “participants” of the NSCC/DTCC are indeed “registered clearing agencies” in and of themselves. (see 3(a)(23)(A) in the smaller print above.)
4) It addresses the FTDs of even market makers held at registered clearing agencies. The bona fide MM exemption from needing to pre-borrow or “locate” shares before making admittedly naked short sales is the main loophole being abused. THIS IS A VERY BIG DEAL.
5) It expressly forbids a crooked clearing firm from “crossing” failed to be delivered shares to a co-conspiring clearing firm in order to reset the 13-day clock. These illegal “wash sales” are pandemic.
6) There is no “grandfathering” in of old delivery failures held in illegal “ex-clearing arrangements” as these are still FTDs as nothing ever got delivered. The mere marking to market of the monetary value of failed delivery obligations has nothing whatsoever to do with making the “good form delivery” of the securities sold needed to accomplish the “settlement” of a trade.
7) In the abusive naked short selling world there are very, very bad guys and other semi-bad guys. The semi-bad guys will probably voluntarily cover their not so huge naked short positions BEFORE the really bad guys will have time to. They may even go net long after covering knowing that their bigger brother bad guys might be in deep doo-doo.
8) All of the crooks are not going to run willy-nilly tomorrow morning and cover BUT THOSE CORPORATIONS WITH IMMENSE NAKED SHORT POSITIONS THAT ARE ABLE TO PULL OFF SOME SORT OF LARGE CORPORATE ACCOMPLISHMENT WILL BE GREATLY BENEFITTED AND THEIR NAKED SHORT POSITIONS MIGHT RISE TO THE TOP OF THE “SHORT POSITIONS TO IMMEDIATELY COVER” LIST.