Python setup.py -> pyproject.toml? Make -> ninja. eBPF kernel modules from C to a custom language. Helm Go templates -> Kustomize.

I am sure there are other projects picking up json from a previous xml + xpath + other ...xml junk.

WirePlumber switched its config from Lua to a JSON variant not so long ago.

there's a rare form of that where it goes from( simple -> programming language -> language with DSL support -> simple dsl ) ; emacs has followed this model a bit.