Sounds wonderful! I am ordering the book, too.
The loathing of older women was there in earlier reincarnations of feminism, at least from the second wave on, and I have many examples of young intersectional feminists saying ageist things about women online without being questioned for that by their contemporaries.
And the link to the rewriting of feminist history is also something I have witnessed recently:
What the second wave achieved is ignored, its faults and flaws are the only part of interest. Yet the people in the second wave were complex individuals, and what that wave achieved and failed to achieve are both equally worthy of inspection.
Still, to me the most fascinating observation is how many lefty men eagerly start Karening all assertive women (and not just white, middle-aged women) when they can do this while pretending to speak for the truly marginalised groups. Just yesterday I saw one tweet about older women soon dying out in any case so their views are irrelevant.
That 'older women' is a demographic group, just as 'older men', which keeps getting refilled is not something they notice.
So yes, one important underlying reason for all this is the view of women's value on the basis of fu**ability. Another may be generational rebellion, but this doesn't seem to affect male-focused social justice movements much, and I'd expect to see it in those, too, if the reason was just in generational questions.