Also; more generally: it makes sense to KISS, and the key risk here isn't somebody using yaml or json or whatever initially - even where experience shows that's insufficient, it's just not that costly either. The question is what to do when that becomes unwieldy. And I think it's pretty clear that kinda-sorta-programming that tries to incrementally extend stuff like static config languages - but only slightly - doesn't work well and is a bad idea. It's inconvenient; it results in many of the same issues as a full programming language, and it's often really inconsistent in its expressiveness - as in, for any given application thereof you're likely to run into limitations.

I think it's wise to try and skip as many of those intermediate stages as possible. Of course; that's not a clear-cut solution strategy either; because what's "as possible"? Exactly how high up the language chain do you need to go; conversely which language (and environment) features are too powerful, rendering the language difficult to contain?