That's the first that I hear of a stack of SIMs that would be active with the same account.
The extra amount of space IS valuable, I never denied that; the question is how much space and how valuable. There has to be a lower limit when it doesn't matter any more. If not 50 mm^3, then how much is this limit? 5? 0.5? How do you calculate it? For reference, 50 mm^3 is the volume of an average drop of water.
Until someone gives me a reasonable argument as to why a 0.08% decrease in the total size would matter, I am going to maintain that this decrease is negligible and not worth redesigning the SIM.
Also, they are inactive cards. I activate them in the extremely rare case one is needed. "Stacks" was hyperbolic, but they basically have never charged me for a SIM card because I refuse to pay for them.