If you think humans are going to start eating a more boring, simplified diet, you are missing a major plot line of human civilization, which continues to give us an ever-increasing array of foods in every possible configuration.
You assumed that eating plants over processed corn/pea protein/soy isolate/canola oil blocks = a bowl of raw spinach. There are endless delicious cultural cuisines which are made of only plants, not ultra processed, and certainly not boring.