That to me feels too dangerous. You'd need to sandbox every piece of config file you use. I've been sketching on a shell/scripting language/system for a while

That to me feels too dangerous. You'd need to sandbox every piece of config file you use. I've been sketching on a shell/scripting language/system for a while and I've been thinking of it being in-effect three sub-languages, one nested within the other. At the lowest level: pure data, middle level: pure functional expressions, top level: imperative commands. I'd think that most use-cases for a configuration file would be satisfied by the lowest level, and some by the middle, but absolutely none would need the highest. Then a config file would be "sandboxed" by the language syntax, with very little risk of it breaking out.