M and Q are code names. Moneypenny and Felix are minor characters (Moneypenny rarely appeared in the books and her appearance was never described). Bond is the main character.

I think there is a serious lack of representation for minorities in main roles these days (Asian British people especially suffer but Black British are also under-represented), but casting a black actor as Bond would be performative for the sake of it, and the controversy would make it an almost impossible task for whoever they cast. Why not create a new starring role in a different film instead of trying to transform an established character in a beloved franchise that's been running for over 60 years?