Coding aptitude clearly exists

The 2006 study I'm referring to is entitled "The camel has two humps", and attempts to establish that coding aptitude not only exists, but is bimodally distributed ("two humps") and can be predicted accurately before the student has taken any coursework or written any code. IOW, that you can discern, pretty unambiguously, who is worth teaching before you try teaching them.

And that is what didn't replicate.

Sure, aptitude exists. But there probably isn't a bright line, or even a bottleneck, between natural coders and everyone else.

Coding is a highly specialized skill not useful to most people in everyday life.

That's what they said about literacy a thousand or so years ago. If you're not a scribe or a priest, why bother? Today, though, a person who can't read is effectively mentally incompetent to deal with ordinary, expected situations in society. Within a hundred years, the same will be true of a person who can't choose and apply algorithms to solve problems. It's not about getting a job slinging Java; it's about being able to tell (increasingly-omnipresent) machines what you want them to do for you.