It seems like you've started with an unusual premise (if a foreigner is otherwise indistinguishable from a citizen, he should be granted citizenship) and design

It seems like you've started with an unusual premise (if a foreigner is otherwise indistinguishable from a citizen, he should be granted citizenship) and designed a test to implement it. Instead of focusing on the implementation, I think it would be more informative to explore the premise. It really makes very little sense to me, especially the "should be forced" part. Who exactly would force all nations to relinquish the most fundamental aspect of sovereignty? To what/whose gain?