reed23, you wrote, "Affirmative-action casting ideas being discussed today in various corners were completely unknown until very recently."
It may be that you meant something very specific and particular by "affirmative-action casting ideas being discussed today in various corners" that is not quite clear to me so perhaps it is not necessary for me to reply. Even if that is the case, I just want to clarify for anyone who may think that casting people of color in roles traditionally played by white performers or that were (probably or definitely) written with white performers in mind or for which white performers might be felt to represent more realistic casting did not start all that recently. It goes back to at least as long ago as the 1940s. Admittedly, at first there were only occasional isolated examples, but even in the 1940s there were at least two examples of new Broadway musicals that cast people of color in prominent roles, as well as in the ensembles, when the plot did not necessarily demand or particularly suggest it.
Bit by bit, over time there was more and more of this. There was movement more quickly and on a larger scale in some areas than in others, and during some periods it may even have seemed as if things were moving backward rather than forward, but it was going on.