1. Business/Income/Making Money
And the many variations of it.
These niches are not "group of people" but basic human NEEDS. Will always be there as long as the human race exists.
And these niches will never get saturated because...
People like to learn from the idealized version of themselves.
So a person in US can create the best ever product on "how to make money with XYZ"
But a person from India would prefer to learn from an Indian on the same topic...
...even if the latter's product is not as good as the former's because people want to learn from someone who are the nearest to who they want to be like in the future.
Just some ideas which I got from Eben Pagan and his coaching programs.