“it will only set the precedent that anyone in the world can run for US president.”
Well, I’m not sure that’s really the point. What matters is whether you can hold the office, which is a very different thing, and quite applicable to the subject at hand.
You can run all you want, no matter what your status, but if you don’t have the prerequisites to hold the office you can’t hold the office.
I don’t think it will work out that way. If it were to become an actual issue, the Democrat Congress will pass a law granting him “Natural Born” status probably explicitly covering both candidates in order to imply that McCain is not Narural-Born. The MSM will NOT publish any of it, even if irrefutably true and the courts will ignore it. If the man be elected without the qualifications, it will be effectively cited in future elections and that clause in the Constitution will have become gibberish.