This is deeply misguided, I think. Dhall is a neat hack, but it's still a hack.
Any and all attempts to munge YAML or to turn YAML into something Turing complete are signals that a scripting language would have been a better fit for the problem.
The exit to this cycle is:
* to use configuration languages for things that are genuinely configuration now and always
* scripting language APIs for things that are genuinely not configuration (e.g. build systems).
* provide both for domains that are genuinely mixed (a lot of kubernetes probably fits into this category - some things are configuration for some people and dynamic or generated for others).
It sounds simple but it is hard - the correct border between config and code is usually hard to perceive and how your tools end up being used is inherently unpredictable.