Yeah, I'm not so sure. Security is about ensuring certain guarantees. If your configuration language is Turing complete, it's easy to get into a spot where you simply can't be certain of the final state of your system. That's not secure. Turing complete configuration language might be an instant red flag, like "perpetual motion" is to physicists.
It's possible to ensure termination of Turing complete languages by rejecting certain programs, but the work required is not something you'll find in a config file parsing library.
Add “ackermann 10 10” to your configuration file and you have something that’s technically proven to terminate, but won’t do so before the sun burns out. No security properties are gained here.
The security property gained is that with terminatation, other sorts of analyses that check security properties of interest now become possible to prove. It doesn't mean they'll be tractable, but "possible" is a necessary precondition for tractable.
It's possible to ensure termination of Turing complete languages by rejecting certain programs, but the work required is not something you'll find in a config file parsing library.