Honestly, having wrestled with YAML, I find it's easy to write YAML and a bear to process it, in that it seems to be a "read-only" format for machines.

Given some YAML file, making any kind of automated change generally nukes the formatting entirely, let alone the comments. I'm sure there are some libraries that do it right, but there seem to be far more that are just awful.

One nice thing about Dhall is that there's a reference implementation written in Haskell where they have very good pretty printing libraries so it's likely that programs would be able to do automated updates to configuration.