Had Star Trek debuted a year or two later, they probably would have had to make accommodations.
Break me a give. It was momentous when the Trek franchise finally put a non-white in the big chair a quarter-century later.
White actors playing nonwhite roles became controversial because it was an expression of racism. Specifically the racist assumption that good God-fearing Americans didn't want dirty Indians and Negroes and what-have-you on their film and television screens. Therefore nonwhite actors were denied work in roles actually portraying their own cultures or were forced to work in ghettoes of largely negative and stereotypical roles. Those barriers began to collapse in the Sixties, but even now we're far from at the end of that process.
White actors do not suffer from any corresponding lack of representation or roles (except to the extent that there is still a paucity of good roles for women). Black actors are not being hired to portray negative stereotypes of whites. White actors are not being confined to portraying witless, expendable sidekicks or criminals or savages. It damages no-one that Idris Elba gets to play Heimdall; this is just another case of certain persons of pallor falsely imagining themselves to be victims of "racism" because other people are finally getting access to privileges they've always tacitly assumed to be rightfully theirs alone.
The idiotic babbling about "political correctness" always has to ignore extremely obvious, simple, plain facts like this.
All of this exactly (I was going to post an explanation myself, but I'm way too fuzzy from a cold to be articulate.)
Also, 'political correctness' is a stupid argument. Without people forcing issues of representation and equal rights, things would never change.