I think Dhall is good at pushing forward some ideas, but honestly I feel like Skylark (Python but not turing complete) just feels like the right way forward. Being able to specify dynamic functionality in a configuration file, when paired with a good configuration API, really makes stuff straightforward IMO. Gunicorn is the best example of this.
We have all of these tools that try to propose declarative configuration, then run into the fact that people really do want dynamic systems with some abstraction capabilities, and then have to overlay that into their systems.
Is skylark (now called starlark btw) general purpose? Its my understanding that its largely used for configuring bazel.