Just snatching a moment while my internet connection is temporarily working to add a futher comment.
One of the big differences now compared to the era JB is so nostalgic about is that at that time given that the BBC and the establishment sort of set what aspirations are, it was inevitiable that people who were not part of the establishment tried to get noticed by it, get invited to be part of it etc..
Nowadays there are many people who probably only have the vaguest idea of what the BBC is, and have aspirations and interests that the BBC probably has no idea about.Let alone the arts events the broadsheets focus on, etc..
Not only has their been a growth in the number of tv and radio stations but of course the internet has given people the opportunity to happily live without any concerns about white middle class values..
Even when I was about to leave school (some decades ago) we sniggered about silly it was that people aspired to get to got to old fashioned events that had grown out of upper class life style. The idea that people's social calendar focused on these centuries old "events" (the boat race!!!! grand national???) we found unbelievable.
Because of the growth in music festivals, alternative art exhibitions and sub culture trends, we no longer have a society that aspires to the in fact very narrow social sphere of the chattering classes.
So maybe the problem is JB has stranded herself in what is now a minority culture (which still has power within decision making groups) and it is just possible that the working class and other minority groups no longer think it is their dutiful role to aspire to the so called heights of achievement of mingling with becoming part of middle class culture.
So in asking what happened to the working class maybe JB needs to ask herself why she has marooned herself in a rather narrow sub culture of those who think 21st century UK still functions under the concept of society that was challenged by the "angry young men" (1950s incels), then 60s hippies, then feminists, and so on. And for man people no longer exists.
In a way it is the older established sports that still cling to an age old class division where working class can achieve recognition etc.. But maybe JB doesn't think sport counts. 