every config parser is a compiler. if platforms (e.g. programming languages) made run-time plugins easier, we wouldn't even have config files.

Imagine a config file with type checking and control flow. You have it-- it's your programming language. you just need to load the code at runtime, like erlang.

You might want to check out Dhall[0], which is a configuration file format that allows a safe-ish subset of functional programming language idioms. Needless to say that it requires a full compiler :)

[0]: https://dhall-lang.org/