I agree with the general thrust of your post [re: individualism embryonically present in class society], but I would like to qualify it, in that to say X is a pre-history of Y seems too Hegelian for me (for it suggests the unfolding of Y is already incipiently present in its original seed X), though I recognize that X must serve as materials (in this case ideological materials) to be used by those who make Y.
Also, here we might make use of Nietzsche, that is, his linking of a genealogy of morality and 'nobility,' in that moral choices are stuff out of which individualism is made, esp. with regard to the line you quoted from John Webster's _The Duchess of Malfi_.
That said, the emergence of individualism may perhaps be more clearly and strikingly illustrated if we look outside the West, in places where pre-modern materials proved to be more resistant to new articulations, thus making a 'break' more necessary (and visible). For instance, I recommend Karatani Kojin's _Origins of Modern Japanese Literature [Nihon Kindai Bungaku no Kigen]_ (Trans. Brett De Bary. Durham, N.C.: Duke University Press, 1993).
Yoshie