I believe the big issue is not just whether the maintainers get paid, but how they get paid and who their boss is when they get that pay.
Frequently, companies are glad to hire maintainers on staff to gain influence over the project. This is usually implicit rather than explicit, and the best maintainers are very good at, effectively, extracting funding from their employer to work on what they think is best for the project. But that's a highly complex political skill that not every maintainer wants to (nor should have to) develop.
This is why I have devoted my career to building charitable infrastructure that can fund development work in software freedom projects. At Software Freedom Conservancy, we have at least seven maintainers from five different projects regularly funded to work on their project. (And there are more, that's just what I could count quickly in my head while writing this comment. Here's a few blog posts that talk about that.
I really believe that where and how the developer gets funded matters. USA 501(c)(3) charities must act in the public good, and do work that benefits the entire public. By extension, developers who work for a charity can focus completely on making the world better with their software, and they aren't themselves (or even work regularly with those who are) required to meet sales targets, or otherwise make sure the endeavor generates revenue for the organization. Ultimately, everything a FLOSS charity does is basic software freedom infrastructure, maintenance, and R&D for the community.
And, this isn't just a pitch for Conservancy. There are many charities where one can affiliate their project and get this done. In addition to Conservancy, there's FSF, Software in the Public Interest, and even Open Source Initiative is looking into doing some of this as well.
Finally, another thing not mentioned in the article that developers often need as much as direct payment for development work is funding for travel to hackfests and conferences (which is also easier to raise money for as the amounts aren't as much). We do that too at Conservancy.
Whoops, "Save" on opensource.com doesn't give you the opportunity to preview before posting it seems. Here's the blog link I was going to include: https://sfconservancy.org/blog/2018/jun/26/highlightsJune2018/