[mkramlich]

I do think the "killer app" use case for the modalities you're talking about are data entry kinds of use cases. Where a non-expert user, perhaps one who has to deal with a variety of formats, very randomly, is required to type things in that strictly confirm to a perfectly-defined syntax. And he/she has a gigantic amount of data to enter manually, by hand, in a short time. Higher throughput is better, but also highest correctness is the other dimension. Tiny percentage time overhead spent on thinking, design, test. Mostly on data entry by hand. Then yes your approach starts to yield disproportionately higher benefits.

Arguably one reason why XML/XSD/XSL took off. It was not just yet-another-structured-text-format like CSV and JSON. It also had an "official" way to express and constrain an application data format, and generic query and mapping languages. Great for low brain, high volume, high repetition use cases. However... programming itself is high brain, lower volume, low repetition.