You see, there is the use case, and their is the market. Blockchain can be applied to every use case possible but what is the demand for such use case? As a developer, you are not only creating a solution to solve a problem, you gotta look at the business part of it. What you are bringing to the market must be what the people want and can attract a userbase enough to attract investments.
And believe me, not all under cases attract the right number of user base. Users is what makes projects grow into business.