The best bet would be to build proprietary paid services on top of the open source infrastructure. See Laravel's projects.
From my personal point of view, the most sustainable way of funding development of free software is through businesses that utilize that software, but whose main business is not that software. The value proposition for the business to open source their software is mainly in getting improvements from outside, and to ensure better integration with other free software. But the main reason to build software should be selfish in the sense that you can directly use it yourself, and not the idea that you could somehow sell the software in some way or form.
There easily could have been an alternate history where Docker Inc was the first one out of the gate with an enterprise kubernetes distribution, been a positive part of the community, and been a success.