You could also use the kelp as a food source and as a food supplement as well
Dulse is quite popular in Northern Ireland if you go to seaside towns. It's very healthy - high in potassium and calcium and good for bones, reducing blood pressure and thyroid health apparently. Dulse is made from a different seaweed from kelp but I can't see there being much difference between them.
The Welsh also eat seaweed for breakfast. Laverbread
Giant kelp (Macrocystis pyrifera) is a very different beast than a lot of other edible seaweeds. But moreover, one major point of this chapter was that the Cooperative Commonwealth mostly abandons utopian food solutions (and open ocean aquaculture is more practical than closed system aquaculture in some regards but definitely still qualifies as utopian, alongside vertical farming and insect cultivation and other things such as vat grown meat) in favor of the much more technologically simple solution of just feeding humans what you would otherwise be feeding to animals (and they also don't focus on increasing yields of those animals as obsessively as OTL's Americans did, owing in part to how food animals are owned and managed).
And while the author talks about them abandoning legibility, which they did do temporarily (or rather, they shifted what is legible to the average American as food)- the means by which they dress up tofu and the other faux-meats here is very much an attempt to claw that back. They smoke tofu, they dress it up in a sweet and sour sauce, they form the ground nut cutlets into the shape of a pork chop and serve it with a gravy. And to go back to the mother-in-law sandwich- they still try to make you feel like you are eating a meaty main! Its hard to see how a kelp salad really finds its way here, in a culture which hasn't even had the shifts of OTL's America towards raw greens (an outgrowth of California Cuisine, health food and diet culture) and towards things like arugula and kale.
My dad was a Chiropractor (now retired), so was very much into healthy lifestyle, nutritional supplements, etc... I remember taking vitamin supplements made from kelp when I was younger...
And you'll note that spirulina (not technically a kelp but an algae and very much in the same sort of health food vogue) does make an appearance in American public schools as a supplement.