I haven't carried a blood card in 5-10 years, nor has my spouse. My spouse has said (more than once) that the logic behind the blood policy is weak at best, and easily argued against...but would still refuse blood when it came down to it. A little confusing, but I haven't ever pushed on the issue.
If this scheme of collecting copies of everyone's blood cards does play out, I'll be curious to see how it plays out in my family.