I can buy the argument for making Bond female, for representation reasons. I happen to think that it's a deeply flawed one, but I get why people would want to argue for such a thing. Where I have to get off the bus is when someone tries to argue that changing James Bond's sex or gender is just a minor flip. That for me is a real sticking point.
Just looking at some of the other variables that have been proposed to change:
On the surface changing Bond's race could be seen as a big change, but in actuality it would probably be entirely cosmetic and make zero difference to any other element of the movie. We already have examples of this. Both Felix and Moneypenny have changed race seamlessly and it has had zero effect on the story or their character.
Since racial dynamics are rarely brought up in Bond movies and also that race is far less politicised in the UK anyway than the US, you could bring in your Idris Elba without any real dynamic change.
Viewers are seemingly able to handle the suspension of disbelief of changing actor for James Bond, and I'm sure they would be able to handle this change too. Background / Nationality
Changing Bonds nationality would constitute a bigger change. Supposing he was an American in the British Secret Service (if that is even possible) then there might be the odd jab at his nationality and it might potentially change some aspect of his nature, but not necessarily so.
Change it so that he's spying for some other nation and that changes most elements of the movies, they will lose their quintessential Britishness which is part of their charm and reason for existing. Much of the dynamics and recognisable elements of the movies would notably shift. However Bond's character could probably remain very similar, the things he does, the way he treats people, the way people treat him.
You could imagine back in the day Hollywood insisting on a US version of Bond, they'd still call him James Bond and maybe people wouldn't even notice the difference. But it would be a big loss to the franchise. Gender / Sex
Ok so you change James Bond into a woman. Well the first thing you need to do is change the name, so it probably wouldn't be 'James' Bond, let's go with the obvious 'Jane' Bond. So from the very start it's not the same character because there is a different name.
Secondly, suspension of disbelief. Would audiences be able to switch over in their heads and say 'yep, this is the same character as the James Bond in all those other movies'. I really don't think they could. There is a clear delineation between men and women and audiences would struggle to see how this is supposed to be the same character. From the start then nobody is able to assume that this is the same Bond as other movies, it's a clean slate. Might be a positive, might be a negative. But it IS a big change.
Ok then, what about Bond's relationships with other people. That would clearly be a big change, especially romantically. We all recognise Bond as this suave sophisticated womaniser, able to seduce the most fascinating and beautiful women in the world, and that is one of the elements of Bond's character that people enjoy the most.
How does it work with a woman in the role? Is she seducing men? Would that work in the same way? Almost certainly not. Like it or not male / female dynamics are not symmetrical. Do men need the same level of seducing by a beautiful woman as the reverse? Do we believe that is the same thing or will seduction scenes consist of some bloke not believing his luck and hurrying to find a bathroom to make out with Jane.
How will audiences react to a promiscuous woman? Will it be the same reaction as to James Bond. While it might be interesting to see that reaction, it doesn't mean audience reactions will be the same. You can at this point compare Bond to Killing Eve, where the main character is promiscuous, but she is a character with massive personality flaws who barely feels any humanity at all, and her promiscuity leads out of that.
Who is she seducing then? Men? Who are these men? Are they dressed sexily? Are the opening credits filled with the dancers from Magic Mike waving their thongs in silhouette? Are these men a bunch of himbos? Badly drawn male models walking out of the sea?
Or is it women? is Jane Bond a lesbian? Well that's a change. How would that work? Will we get a bunch of scenes of women turning her down because they aren't gay. How does her sexuality change the dynamics of her character.
Then there is the misogyny. How does this work with a female? Does she become a misandrist? Is she dismissive of men, does she treat them as set dressing? Does she use her physicality to over power men in the bedroom? Or is she dismissive of women? That would be an odd change.
Plus if you want to add in some more feminist points to the movies you might want to start bringing up how women are treated differently, how does she deal with authority, how does authority deal with her. Some people might be nicer to her, some might dismiss her. Every single interaction she has with people might have to reflect that she is a woman. But then would the nature of the movies change dramatically to become some political think piece instead of mindless fluff.
Then there is the physical element of it. Most Bond's are played by tall, physically imposing actors, people you could imagine could go toe to toe with the Henchmen of the world. Craig is shorter but really bulked up for the role. A woman would be much smaller than most of the people she fights, she would have to find other ways to take people down. Would audiences be ok with the amount of violence inflicted on James Bond if it's a woman. What about the notorious torture scenes,especially to genitals, are we ok with those?
Then what does Jane Bond look like. The iconic shot of Bond wearing a tux and holding a Walther PPK.. well that has to change. Will she wearing a tux? If so, why? Is a woman wearing a tux and a man wearing a tux sending the same message? Does the iconic shot even exist any more?
Is she walking around in fantastic dresses all day by top designers? Does that mean the same thing. Is she allowed to wear skirts? Is she rough and ready looking like a Daniel Craig... if so how does that still stay glamourous and attractive if it's a woman. Like it or not men and women are judged differently when it comes to physical attractiveness.
Then there's the problem of Bond being a male fantasy figure. He is notoriously 'the man that men would to be and women want to be with'. Cast a female and suddenly that is flipped. Actually it's not flipped, because it's unlikely to work the other way around. So who is the movie now for?
So it seems to me that whatever the rights or wrongs of gender bending James Bond, it would always be a massive change, and I can't imagine anyone being able to accept that it is the same character as the James Bond they already recognise. It would always be seen as a different character. So while you might be able to keep a number of traits of the character and tropes of the story, there would be so much that would have to change that nobody would be able to accept it.
Also it would just be a deeply unpopular move. Nobody really wants to see a female Bond, except for Pierce Brosnan, and if we got one and then the movie dies on his ass and is an enormous bomb, what does that do for 'representation'. It would set back the cause by decades. So it's a movie that absolutely HAS to succeed. That's why it would never happen.