The result was an nREPL middleware named
whidbey, which replaces the normal print-method rendering with any rendering function you care to supply. I've submitted a patch to REPLy to support this, but it still requires jumping through a few hoops to get set up. The README gives a pretty thorough rundown, so I'll defer to that.
I'm hoping some of you will feel adventurous enough to try this! Anecdotally, having REPL output colored and pretty-printed by default is really nice, and I'm looking forward to getting this better-supported by Leiningen/REPLy/nREPL. Please let me know how the setup goes and any issues you run into.
Greg Look