i think the point he's making in that post is he does have the time, and more importantly the passion and will to do so. the compensation he was receiving for having to work at a large org wasn't fair, and that's why he's changing directions.
I've seen a guy who worked full time on open source have a Patreon, which had a few big sponsors that would pay / donate $5K or $10k / month - that's another good option IMO. Although I'd donate it directly to him, instead of having Patreon scoop off their share.
For most companies, the proposition for open source is that you get something of value for (almost) free. If you start paying someone to work on that thing the equation becomes more complicated. Now you are competing with 1) A different flavor of free (another project) and 2) Non-free but with an SLA that you can count on.