I don't think I currently do, but that's sort of my point: people don't want to do this, for reasons ranging from the income left on the table to the type of work not being fulfilling.

Note that both of these are handled by the premise, which was that OSS maintainers would be materially unblocked to focus on OSS by a UBI-level income. This assumes that there are a non-trivial amount of OSS maintainers that don't care about the couple hundred thousand dollars they're forgoing, and that they have at least 30 hours of their week filled with fulfilling work.

Tangentially, I match the motivations you're asking about, but not the exact implementation. I spent the early half of my 20s with a far higher income than I wanted, and definitely didn't (and don't) enjoy working 40 hours a week. Given how motivated I am by intellectual challenge, I came to the realization that it was damnably hard to find a job that would give me a suitable intellectual challenge but not require me to be full-time. I "solved" this by interleaving 2-3 years of working with 1-2 years of travel/personal development a couple of times during my 20s.

That’s probably how most people do that. I have to admit that programming less than full-time was hard for me, because I tended to go flat out. And then burn out, LOL.