I wouldn't call KDL "established"; it's honestly pretty niche. It looks _similar_ to pre-existing configuration formats, but KDL is very picky about syntax. I.e.: single word string MUST be quoted.
In this same space, https://codeberg.org/emersion/scfg/ is pretty widely used. The curious thing about scfg is that it's not really a "new" format: the syntax described has been in use by different tools for decades. They just didn't call it scfg, and it's mostly the name itself that's new.
> picky about syntax. I.e.: single word string MUST be quoted.
Seems like the opposite:
Example from kdl website without quotes
package { name my-pkg
Example from scfg with quotes
train "Shinkansen" {
It is picky, but picky is good. It's explicit which creates uniformity.
For example with niri, if you forget quotes on a string value, you get this error.