I think this is reasonable in some contexts but it depends. Often the configuration is done by a different person or in a different context than the development

I think this is reasonable in some contexts but it depends. Often the configuration is done by a different person or in a different context than the development. The configure-er may or may not be a programmer and the deployment environment may or may not have xyz programming language available, etc. The JSON superset aspect nicely supports spitting out JSON from a script when people want to do it that way. HOCON is nice when for example you just want to sub in a couple of env variables or avoid a little cut-and-paste.