Came here to say similar. In particular dhall does allow scripting (functions etc.) but is non-Turing-complete as a feature. This seems like a particular sweet spot to me as it allows for more dynamism than data formats like json/yaml while constraining the scope sensibly.
It also has very nice bindings with haskell and nix
It allows each line to be completely independent of it’s neighbors; you can comment and/or add lines without needing to touch neighboring lines. Also, it makes it visually easy to spot missing commas. Give it a try sometime, it’s actually quite nice.
Having prefixed commas is a rather common style in the Haskell community, because it ends up nicely matching open/closing brackets/braces and lining things up.
Since the author of Dhall comes from the Haskell community, he's kept this style.
It also has very nice bindings with haskell and nix