...And what happens when Idris Elba picks up the Bond mantle after Craig is done ?
Well, to draw a contemporary parallel, what would happen if the Star Trek producers cast a very short, obese man with tight curly red hair and a Jerry Lewis voice as Mr Spock?
The paying audience has a right to expect that the fictional character with which they're very fondly familiar is going to remain the same, (in fact, exactly the same), when they put their money down and walk into the cinema. If filmmakers significantly change anything about the character as originally conceived, they're taking money under false pretences.
It's a simple as that, and has absolutely zero to do with "racism" or "sexism" or any other "ism".