I wasn't even considering cyanide. I was thinking about all the healthy things there might be in sea salt, for example, that might retard development or worse. You don't usually want iodine in developer, nor some other things that are just fine for human consumption. After all, our bodies contain at least traces of nearly, if not all the natural elements, and by now maybe even some of the unnatural ones. I would not hesitate to eat Kosher salt any more than I hesitated to eat those delicious Kosher dill pickles a while ago.
Truth be told, I did some experiments a while back testing the use of salt in developers and decided it was not worth the trouble. These were reported in the article "Salt to Taste" in Photo Techniques. That was when I found that 4 grams of sodium ascorbate did more good in a liter of working Rodinal than either salt or sulfite. You might find the same to be true of D-23.