WWOOF is a marketing term / organization for what amounts to being an intern on an organic / permaculture farm.
I've done some fun genealogy and per census records going back centuries young people have done this kind of thing, so as long as organic / permaculture farms still exist, our kids will be able to intern if mutually acceptable.
Beyond peasant labor there's an implied educational aspect where most WWOOFers want to run their own farm some day and are touring around learning how. If you're not learning anything new anymore, its time to move to the next farm. Unless you got a masters in Ag Sci its probably not a fair comparison.
In the ancient apprenticeship structure, its basically being a journeyman in the field of organic farming.
I've read a lot about it from having a goal of redesigning my backyard according to permaculture guidelines, although not having the time/weather/money combination optimized to really accomplish anything. One of my neighbors has an excellent permaculture designed backyard, which is both appealing to the eye and interesting to think about.
There's probably a startup idea involving WWOOF as a template for other fields of endeavor. Probably not hyperregulated field like becoming a surgeon, but maybe something a little less regulated like a tree-surgeon or something in tech. A formalized online group to help "guide" the internship process in tech or maybe media?