What the Euro proof houses have going for them is history, they date back to muzzleloading cannon and matchlock days. They developed proof standards for every cartridge that's come down the pike for the past 150 years.
Here in America we have been enjoying the fruits of a free society where invention and innovation has spawned hundreds of firearm designs and thousands of cartridges. Who will decide what the proof load for a 38-55 Winchester will be? How will it be determined, do you blow up a bunch of Ballards and Winchesters?
Do we adopt out of hand, UK standards(Obama hates England)? What about all the wildcatters, do they become outlaws? Does the guy who AIs a 6.5x54MS have to have his rifle blown because the proof house has never seen one?
The rifle stuff is much more complicated and far reaching than the shotgun implications.
Jim