I think you need to examine niches carefully.
I was able to create an open source piece of software that allowed me to sell over $50,000 worth of ebooks (training manual) over the course of 5 years. Eventually I was able to sell the entire software for a small five figure sum.
The money involved was not huge but it was great to have. Users did not care that the software was OSS. They cared that is solved a problem and the ebook I sold made it even easier. That is how OSS makes money - by solving problems.
OSS is not a business strategy, it is just a software license. You do not "make money" by adopting a software license, whatever it's moral merits. You need a business that solves a problem and OSS can be part of that.
The money involved was not huge but it was great to have. Users did not care that the software was OSS. They cared that is solved a problem and the ebook I sold made it even easier. That is how OSS makes money - by solving problems.
OSS is not a business strategy, it is just a software license. You do not "make money" by adopting a software license, whatever it's moral merits. You need a business that solves a problem and OSS can be part of that.