For example, this graph shows how staple words of leftist thought, such as "socialism," "racism," "sexism," "feminism," "discrimination," and "civil rights" have been in decline in published books over the last decade. Socialism peaked in usage around 1976, but most of the others enjoyed their peaks in the 1990s. (To be precise, discrimination had a peak around 1975 and a second one of equal magnitude around 1996. The other four words peaked in the 1990s.)
Is this just a decline in the proportion of public affairs books published? (These numbers, by the way, are weighted by publications, not by sales.) I don't think so. In contrast, "capitalism" and "conservatism" have been relatively flat since about 1980, and "evolutionary psychology" skyrocketed from 1992 to 2004, then drifted slightly lower. "Darwin" was flat from 1960 to 1990, the shot upwards until about 2005.
That fits my general recollection of hanging around bookstores on my lunch hour: that their was a surge in DiversityThink in books around 1989 to 1995 (perhaps related to the collapse of socialism channeling leftist thought into other directions, perhaps related to the surge during the Crack Era of bad behavior among blacks creating a perceived need for more denunciations of white racism). This era was followed, however, by collective boredom and embarrassment.
The word "diversity" itself zoomed upwards starting in 1989, peaked around 1999, but has only dropped slightly since then. As a non-accusatory happy word, it doesn't inspire as much heretical thought as an accusatory word like "racism," so it's more likely to endure in exhortatory prose.
We're now well into the Brezhnev Era of DiversityThink, when everybody is bored and cynical about the ruling ideology, but it still has 53,000 tanks, so most people assume it can't be all that off-base.
To get off topic, how about Nabokov v. Borges? VN took the lead in mentions early this century, only to to be overwhelmed by Borges in the last few years.