My question to you is this:
Who is supposed to enforce the NBC clause, and at what stage of the process?
For example, there is no “running for President” in the Constitution. There is also no “voting for President”.
If an non-NBC were on the ballot, and won, say, California, would it be the responsibility of the Legislature to not appoint the relevant Electors? Would it be the responsibility of the Electors to vote for someone else? Etc.