These types of cases are actually pretty traditional, especially for McKinsey. The reason why people think that they are rare is that the casebooks (that are in general not a good source of cases) almost don't have them
Feel free to reach me if you need a prep on them.
To provide a bit of structure, there are several types of non-profit cases:
- Factors influencing the price (What are the factors influencing the price of oil? Factors influencing the price of real estate?)
- Macroeconomic cases (How will you improve life expectancy in a particular city? How will you decrease the unemployment?)
- Public sector non-profits (Increasing the revenues of a museum; increasing the revenues from tourism in a city)
- Redesigning the processes (How will you develop a new anti-monopoly regulation?)
- Non-profit investments (A billionaire is building a new school. What are the factors to look at?)
- Ops and cost-cutting (How to reduce the traffic jams on a bridge? A garbage processing facility is out of capacity, what should they do?) - I personally consider them as a separate type of cases that is pretty traditional in the offices performing a lot of ops projects.