"but most of it would never exist, even if the technology was readily available. "
What makes you think that? My personal opinion of marketers is sufficiently low enough to assume they'd go to any lengths to sell their product. 
Because I believe that most of the behavior of the products presented here would be counter-productive. First, marketing can change human behavior, but it can't change human nature. Rather, it is designed to exploit human nature to maximize returns. People have been shown, throughout history, to react better to marketing when it's non-obtrusive. Snack cakes places at specific points in the store where they are judged to be most attractive? I can see that. Snack cakes talking to customers, even after they are purchased, and products jumping into customer trollies? That's just drawing attention to the marketing.
Second, as I mentioned in my earlier post, it seems that for a lot of the details in this story - the quick reshelfing, the hover-trollies, etc. - the economy just won't work; if you spend more on marketing the snack cake than it costs, you are wasting money. If this was an expensive luxury item, I may feel differently, but if you've managed to create the impression that buying a snack cake is a big decision, then you've already lost the marketing battle.
Third, marketing is about generating habits, not selling individual items. Everything in this story is putting a lot of effort into selling one snack cake, and once the snack cake is sold, it starts putting a lot of effort into getting eaten. If this was anywhere realistic, once it was sold it would start making the customer want to buy more snack cakes. The customer already paid for it, the effort should be in getting the customer to pay more money.
Fourth, the way manufacturer consolidation works today, each manufacturer generates a large range of products. If a customer is on a diet, the snack cake would be a far better money generating object if it was telling Linda to buy its cousin, the equally delicious low calory snack cake next door, and indeed switching to its related line of diet products; diets are a source of greater income for food companies, not less.
And so forth and so on.
This story not only takes some aspects of our current consumerism society to extremes, it also ignores equally important aspects of consumerism. The system that it describes would never take place, because it depends on a large expenditure of effort for moderate returns, while the economy is moving towards lower expenditure of effort and greater returns.
