I definitely appreciate seeing people take initiative within the open source community to keep maintenance alive for packages that are used by thousands of projects. Was any effort made to contact the original author ever? Seems very odd to see them drop off the face of the Earth like that with such a popular project.
Ah, I guess I should have described that in more detail.
The author habitually never commented on the issue tracker, despite continuing to merge pull requests until 2023. An explicit query (https://github.com/okunishinishi/python-stringcase/issues/42) went unanswered, too. Someone highlighted the author's email address on https://github.com/okunishinishi/python-stringcase/issues/43 a few days ago and nothing seems to have come of it.
This is arguably not the strongest possible evidence - and that's why they're so careful about PEP 541. And in all honesty, this is not someone who's "disappeared off the face of the earth" - just someone who doesn't appear to be reachable WRT this project. But I'm not convinced the author ever realized the project's popularity in the first place. It also looks like said author mostly uses Javascript, anyway (https://github.com/okunishinishi?tab=repositories). I imagine the expectations are different in the NPM ecosystem.