Hmm, I guess I have seen datascript / datalog. My main question is more about how many articles seem to suggest that it's basically par-for-the-course in lisp programming to just make a DSL in your projects, so was wondering when that might actually occur.

As mentioned in this list, Ihaka and Gentleman's R implementation of S begain like this but quickly grew into a larger system. R's source code today is still full of lispisms.