This WIP article explains very well the USP of D:
http://erdani.com/hopl2020-draft.pdf (section 3)
This article highlight the value of "design-by-introspection" applied to a particular problem space: https://blog.thecybershadow.net/2014/03/21/functional-image-...
This talk present a concrete example of such: https://www.youtube.com/watch?v=LIb3L4vKZ7U (mind bending stuff)
You might not understand what is new about it, but soon your competitors will understand it.