As far as casting goes, I have exactly the opposite idea from what you wrote. First, I guess I don’t create characters whose gender, age and race are interchangeable. I’m not sure it’s a reasonable goal.

My belief is that if I want to represent diversity (typical of Durham NC where I live) I have to make the choice that a given role should be an actor of color and then look for that person. Most of my work recently deals with families, so it’s not simple to ignore / bend racial lines without planning. I think casting by “who shows up” runs the risk of implicitly favoring the communication networks and social history of people I already know – which may not have the desired result. I think “filmmakers” (meaning you and me) have to commit to the world they want to portray and then make that happen.

Check this out. Steve McQueen asks a compelling question and listen to the silence. No one accepts his challenge. A room full of successful white filmmakers hiding behind privilege. Every one of them, a coward.
http://blogs.indiewire.com/shadowandact/steve-mcqueen-shares-his-thoughts-on-hollywood-directors-not-hiring-black-actors