This doesn't answer the spirit of your question, but regardless of the product/service, I would build a company with an emphasis on employee happiness (which also doubles as a recruiting tool):

- Full-remote

- 4 days/week instead of 5

- 2-3 months mandatory PTO

- Bootstrapped

This isn't lofty or anything, it's really what I aspire to do some day soon. To me there are few sane reasons to build a company predicated on the 40 hour work week in an era where work is intellectual and not based on quantifiable throughput (like working in an assembly line). Today, I would gladly take a 20% paycut to work 20% less per week (e.g. get Fridays off), and so I'd want to build a company in the same way.

I personally think the world is already headed in this direction (with remote work being the first big change).