Note: The answers in this section are conjecture.
Why do you think recent Georgian cookbooks have often not included recipes for solyanka? (connected exhibit)
I think it might be because solyanka is not exotic enough for these cookbooks. These cookbooks purport to show traditional Georgian food, something less known to Americans and Europeans. Solyanka doesn’t fit this ideal as it is more Russian than Georgian, and is also something made out of a more “normal” combination of ingredients (I think the Georgian version is less daring flavor-wise from the Western European or American ideal of a beef stew).
What makes solyanka distinct as a dish from other soups or stews? (connected exhibits)
While I wrote down what ingredients solyankas share with each other and also asked my interviewees to explain what made solyanka distinct from rassolnik, their answers were all very different. There was no universal answer, so I don't really feel comfortable giving one, aside from listing the ingredients that the recipes tend to share.