However, Clojure's equality semantics only really help in some niche situations (where you want to be able to use ints, floats, and bignums interchangeably, mostly), so making the equality semantics configurable would be a huge win for all sorts of applications.
Also, lookup is not the only performance win that CHAMP offers: https://github.com/lacuna/bifurcan/blob/master/doc/benchmark.... One thing the approach makes possible, which wasn't explored in the paper, is the ability to do union/difference/intersection operations structurally, rather than just iterating over each element in the set.
None of these improvements are so overwhelming that they take priority over everything else. Clojure's data structures are still really well made. Given how data-focused the language is, however, I think these improvements are more compelling than everything that's been added to the language in the last five years other than `clojure.spec`.