Hello! I live in Japan now, but am originally from Europe (half UK, half France) so I know most of the vegetables you mention. Salsify -- or salsifis in French -- is still not as well-known as carrots, but it is a staple of French cuisine and regularly features in restaurants: anybody half-way serious about traditional food will know it, I would say.
As for dandelion -- pissenlit in French, which means ... to "pee in bed," inreference to its duiretic qualities -- you can buy it it high-end and slightly hipsterish greengrocers quite easily. Same in restaurants: it's regularly used in salads all while it's in season. I've got one cultivar I'll be sowing later on this year (for both leaf and root harvests): it's called Amélioré à coeur plein "improved, with full heart".
As for the last two, I know them a little less, but I would still say they are relatively common somewhere like France, where they both grow naturally along the coast of Brittany.
Ah thank you for your perspective. I was hoping someone from Europe would chime in and I appreciate your words! It's not surprising that you know many of these plants I listed, but I am also hoping they will catch on more in the US. In hipsterish circles here, too, dandelion is also catching on, but most Americans will go to great lengths to suppress it, pull it up and kill it with chemicals!
Also happy to hear you're familiar with the last two. Sea Kale is becoming very popular in permaculture circles here, but to the average gardener it is unknown. I want to change that!
Thanks for stopping in :)