philzook you are rapidly becoming one of my favorite bloggers! I don't have anything to add, really, I just want to encourage you. Your content and style are awesome. :)
I'm very unfamiliar with this, but are Kanrens similar to Answer Set Programming? with ASP programs you generate a set of symbols, define relations between them and then filter out wrong answers with logic formulas. It's a prolog-y dialect that gets solved with something like a SAT solver.
A good question. For reference, here is a link to an interactive version of evalo being explained http://io.livecode.ch/learn/gregr/icfp2017-artifact-auas7pp Very intriguing stuff. I have not studied evalo in depth yet. I am curious about the relationship between evalo and higher order unification.