It was just, in general, the thought that each family of traits has different times when they are most useful, and (at least in theory), a master of the art could bring the right ones to bear at those times.
Indeed, Musashi would have to have been an Avatar, were he transported to The Last Airbender's universe.
My first major question about this very interesting conceptualization of Avatar would then be: is being an Avatar just a one-in-a-million trait (assuming the population of that world is a million)? Because it seems like a rationalist Avatar would prefer not to be the only one on the planet.
I've been enjoying reading Less Wrong fanfiction, and I wanted to suggest another fandom that should have at least one rationalist fanfiction: Mage: The Awakening. It's a roleplaying game about "modern sorcery." My description can't really do it justice...