I have no problem with changing Mary Jane's race. But what worries me is the rumors that she's a glasses-wearing geek girl or something similar, and we're not getting a proper adaptation of what made MJ so interesting. Honestly, I can't think of any adapation that really did her justice outside of maybe Spectacular Spider-Man. Not even the first movie.
MJ, to me, was interesting because of how she foiled Peter. After the abuse she suffers as a child, she wears a metaphorical mask, becoming a cheery, ditsy party girl to hide her trauma. In contrast to Peter, who wears a literal mask to confront his responsibilities, MJ wore hers to escape from it. And a couple of adaptations have touched upon her upbringing, but none of them went into the parallels between her and Peter, how she coped through her sadness by putting on a happy face and putting herself in the spotlight. What makes her romance with Peter so great is that it isn't just him sharing his secret with her, she does the same, and unmasks herself to him.
And the other problem is the one Marvel has seemed to have with MJ for years, and that is because she's a pretty supermodel and a party girl, she's not good enough for Peter. Several writers have even actually stated that Peter marrying a supermodel makes his life "easier" as if she wasn't an actual character, and just a prop to make Peter's life easier, and that's much more problematic than this whole reverse racism argument. The idea that Peter needs a geek girl, someone interested in science, or the like all seem to be based on the idea that because MJ is conventionally attractive, she's a stuck-up *****, she's too shallow, she's not right for Peter and only loves him because he's Spider-Man.
And really, that's part of the whole reason why MJ became such a breakout character. She wasn't designed to be Peter's love interest. She wasn't a reporter assigned to Spider-Man or his nurse or science partner. She was a girl with her own life and her own interests, and her romance with Peter wasn't destiny or being perfect for each other, it was an awkward accident of two people learning to open up to each other. That's the biggest reason why MJ became so popular. She wasn't a love interest. She was her own character, who fell in love.
And there's no reason the above can't apply to a black MJ, or an Asian MJ, or a hispanic MJ. But Marvel seems to have had a stick up their ass for years about her, and that Peter can't be with a pretty popular girl because that's too easy for him. And that's what worries me about Homecoming, and I'd be worried even if she was a white girl, because MJ isn't a geek girl, that's completely changing her character.
But that's just a rumor. If they're not real, and she can finally do MJ's backstory justice on the big screen, then I'll happily accept Zendaya as Mary Jane. If the rumors are true, then it's just one more time Marvel shoved MJ into a corner.