"The great enemy of truth is very often not the lie - deliberate, contrived and dishonest - by the myth - persistent, persuasive and unrealistic . . . We enjoy the comfort of opinion without the discomfort of thought." - JFK
If you review some past NPRMs (specifically any dealing with fireworks), you'll see comments from the manufactures and organizations about outrageous costs and unpractical implementation, then an ATF 'reply' which boils down to "tough, we think it's safer".
There is no doubt in my mind that the 1/2" shackle rule on paddlelocks will be enforced, along with the rest of the crap.
7/16" seems to be a standard "extra heavy duty" size... I wonder if that's why the BATF picked 1/2" :) It almost seems like they want to be sure that nobody _can_ (officially) lock up their supplies of Explosives "properly": that way they have a nice little "technicality" to write up anyone, anytime...