A 90 IQ is probably a decent rough measure at this point, because that's about what it takes to handle a cash register or a grill. And when the those jobs are gone, it will inch up, 91, 92, etc. But forget it. Look at the future this guy has concocted in his head:
The main fields of human endeavor will be culture, arts, sciences, creativity, philosophy, experimentation, exploration, and adventure.
...it's like he's never met anyone who didn't attend a top tier university. Here's reality:
The main fields of human endeavor will be copulating, hustling, consuming low-brow entertainment, eating, and the occasional lunatic running amok.
...and honestly, we're square on that path right now. There are huge numbers of people who are literally useless eaters. Go to a Wal-mart supercenter sometime. Huge big fat people buying candy, soda, potato chips, frozen meals--often paid by the public dole. I'm not even complaining. Unless you start a sterilization program (and we aren't) it's the unavoidable present and future.
While I don't share the pessimism or sense of superiority one might read into OP's post, I think their point remains (somewhat) valid.
There are many people who 'endeavor' exactly the way he describes, many more than I always wanted to believe. And many of them are quite intelligent, so it's not just about IQ.
While changing our approaches to education and the right motivation, in my opinion, can bring people much further than some of us are inclined to believe, this is a limited solution for all the grownups who live in the way OP describes.
The main policy point made in The Bell Curve by Murray and Herrnstein was about how important it is to provide people with a valued place in society. Without purposeful work and meaningful social integration you inevitably get the sort of degeneracy we see spreading. About six pages of The Bell Curve touched on race, so of course that and the ensuing screeching is all anybody remembers. The real social commentary in that book is turning out to be very prescient.