I happened to have a long discussion on the topic of data businesses last night with a friend. We brainstormed datasets that would be a combination of hard/expensive to obtain while also having resell ability to thousands of customers who would be willing to pay a high value for them. I don't want to get involved in datasets that are easy to obtain (too many competitors, no bar to entry) or datasets specific to a particular company (too much dependence on a small set of customers, cost of acquiring new customers also includes cost of acquiring data, no economy of scale).
It's easy to start with the tech problem: how to collect, clean and analyze data. But reasoning backwards from the business side is much more difficult. Expensive data I can sell once feels easy. Cheap data I can sell frequently feels like a race to the bottom. Expensive data I can re-sell 1000s of times to a niche audience feels like a perfect middle ground ... I just can't think of any examples.