I have no problem at all with anyone having their own theory and using it as a guide for who they believe is eligible to be president or vice president and who is not eligible.
Your theory is in line with the U.S. government’s position in the landmark Supreme Court decision from 1898, U.S. v Wong Kim Ark. The government’s attorneys asked the Supreme Court: “Are Chinese children born in this country to share with the descendants of the patriots of the American Revolution the exalted qualification of being eligible to the Presidency of the nation, conferred by the Constitution in recognition of the importance and dignity of citizenship by birth? To hold that Wong Kim Ark is a natural-born citizen within the ruling now quoted, is to ignore the fact that at his birth he became a subject of China by reason of the allegiance of his parents to the Chinese Emperor.”—Government’s Briefs US v Wong Kim Ark
My theory is not that literal. Posterity of We the People does not mean the direct descendants of the original citizens.
"We the People" is a term of art to represent the citizens at large - at any time. The Posterity of We the People means the children of citizens. A foreign-born naturalized citizen becomes one of the body of We the People, and then their future children (their posterity) are natural born citizens.
-PJ