Dandelion is a good and nutritious plant, even used for medicinal tea. I like it; its taste is a bit grassy but I don't mind that, it 'tastes healthy' if that makes sense, and it did help me to feel better. I'm not claiming any medical facts; people can look into it if they want to. This is merely anecdotal and is a layperson story.

If they proliferate so easily that's a risk if you don't want them everywhere but yes, cultivated carefully, they are a cheap and nutritious resource. I just didn't want them to overtake anyone's yard like kudzu. So I would say grow cautiously, and also, avoid if pesticides were used. (There are natural gardening methods and natural yard care methods. British royal gardens use some such methods.)

So if done carefully this could be a plentiful resource.

As for a foraging menu I agree but it couldn't be a chain type of restaurant. Those are so widespread and in so many varied settings including very urban, and many rely on constant shipments of frozen, packaged foods.

But as an artisanal greens type of salad, yes. But I felt OP was talking about chains. If someone did make a restaurant featuring retro "Depression era" foods then they'd have to present it in a positive way. A lot of our relatives or ancestors had painful memories from that time.

Many of the other foods resorted to by those who had no real access to food or money, and food banks did not exist then AFAIK or not in all cities, were not nutritious nor filling. Mock apple pie is made from crackers. There were people who could not buy crackers, or bake any type of pie. They ate ingredients as is.

And yes it was global but I only know much about the experiences of Americans during that time. No one from elsewhere has confided stories in me.

Also if anyone forages be sure to educate yourself very very well first. Some mushrooms are toxic for instance. But yes it's a way people ate for centuries and still do.