There appears to be a regression introduced somewhere along the line that prevents overriding the printing of objects. (If you look in the code history you can see that this was previously possible.)
Whatever the root cause, we currently have a check for implements? in pr-writer-impl but not a check for satisfies? before the object? branch is taken, which prevents code like the following from working:
In Clojure, you can override the printing of objects with code like
Any associated tests should go in the cljs.extend-to-object-test namespace.