Hyphenation of multi-word nouns is a process in English that usually happens after some time of usage as separate words. It often happens before eventually merger into a single compound word noun. Such as: "Electronic Mail" to "E Mail" to "e-mail" to "email".
Given how often it is used as a jargon term in software development, I can absolutely see this usage of "use-case" here as a "vote" for the next step in the process. Will we eventually see "usecase" become common? It's possible. I think it might even be a good idea. I'm debating adding my own "votes" for the hyphen moving forward.
