Every time I see this I'm hoping that it has taken off, because it feels like such an obvious improvement. Instead of that we have some support for it in FreeBSD, and a homegrown solution in some packages like util-linux. Yeah, there are some concerns, but the concept seems sound and the implementation can be iterated upon.
For instance, years later and it still isn't packaged in Debian. If nothing out of the tens of thousands of Debian packages has a dependency on it there presumably must be a good reason.
It strikes me as one of those libtermkey¹/libvterm things where Leonerd pushed it for years before anybody really used it, despite it being a seemingly obvious improvement over the status quo.
My google fu is failing me right now but FreeBSD also has a shared library used for reading/parsing config files and providing either a common or universal dsl for all conf files using the same library. This is one of the benefits of using an OS instead of a distribution - all the tools are developed holistically and refactors such as providing a shared, universal input or output format, sandboxing everything with capsicum, etc across the board are much more possible.
EDIT
Remembered it. Surprised at how bad Google was at finding this, though!
UCL - Universal Configuration Language [0]. Introduced in a paper by Allan Jude in 2015 [1]. Man page: libucl(3) [2].
[0]: https://github.com/vstakhov/libucl/
[1]: https://papers.freebsd.org/2015/bsdcan/allanjude-ucl/
[2]: https://man.freebsd.org/cgi/man.cgi?query=libucl&sektion=3&f...