"After all, working memory is common, but greatness is rare."

So...it must just be a combination of many factors. Inherent intelligence or working memory can be useful, but so many other things influence whether you become "great" at something...unsurprisingly.

The papers linked to were interesting in how they looked at the different domains (poker, piano sight reading). I mean this certainly is an interesting thing to study, but I don't imagine there will be some proven way to achieve greatness any time soon rather than just deliberate hard work or something. Or maybe there will?