I might just be a simpleton -- I never had the resolve to try an ambitious project in Clojure. I was not aware that you could get full OOP though, what you are describing feels like yes technically possible but kind of a hack to get inheritance / no type hierarchy enforcement. I'm no expert on the language though

I actually disagree. Once you remove the cruft and crap of the involved syntax, good OOP design tends to look damn close to FP design. So I flip your point of view - class based OOP is the hack - despite not really using Clojure or FP in my dayjob or hobby projects anymore. Most fun I had with OOP was definitely Common Lisp though.