Steffans Personality Blog has the interesting idea of adding Tribalism to the Big Five personality measures. It clearly exists, but does not fall into any of those categories.
A lot is going to have to go into this, of course. Can folks become less tribal or more over the years? Can they switch tribes (because of marriage, geography, profession) and retain the same intensity, or does the leaving of one tribe make all subsequent identifications weaker?
Looks like fun.