Dr. Kelly’s thesis specifically entails societies on the verge of moving from hunter/gathering or semi-nomadic lifeways and beginning to settle into farming and agricultural-based modes of living. This timing quirk is more responsible than other factors in determining which societies would have been “first”. I don’t recall that she invokes Jared Diamond’s thesis from “Guns, Germs and Steel”, but it’s far more likely that the ordering is a function of geography and environment than anything else.
Her theory (and an incredibly well supported one) about Stonehenge as a memory palace becomes primary over the other Stonehenge ideas and in some sense those others actually become supporting pieces. Her theory also has incredibly important implications about how we should reframe our cultural viewpoints of indigenous societies from a sociological standpoint particularly including their religions/mythologies.
If you hold the most common current western cultural conceptualization of a mnemonic device, then it is likely a very limited and narrow one. More advanced views that include the method of loci, the Major System, Person Action Object (PAO), and the several dozens of generally “new” indigenous methods that Kelly describes will provide a much more expansive view. As a result many of the astronomical calendars in history are simply time keeping devices and do not serve as mnemonic ones. Stonehenge is one of the exceptions, and even in cases like it in which there are dual memory and timekeeping uses, many of those locations were reasonably far from population centers and the ritual visiting of those sites would have required timekeeping on the local peoples’ parts to know to travel to visit those structures for their rituals, which I now firmly believe were more memory-focused than religion or burial focused. (Relatively few graves were found at Stonehenge.) In fact, I might go so far as to hypothesize that a modern American is more likely to have more bizarre and less useful religious beliefs and practices than most indigenous cultures we’re aware of. Sadly, evidence of ancient cultures’s religious practices is too sparse to do much with.
For some quick/short introductions to her work, you might try an excellent podcast she did with theoretical physicist Sean Carroll or the too short TED Talk she did a while back. From an experimental perspective, you could actually directly use some of the methods she describes in her book Memory Craft with your kids and see some pretty quick results. It also might make for some fun, quality family time.