I think with a lot of these, what happens is often that optimizing the Clojure compiler for those doesn’t matter necessarily, because the JIT might already optimize those.
I think the best improvement to the compiler (but one that would be a huge undertaking), would be to group functions and vars under the same class file, because class loading really slows down startup time, if an entire namespace could somehow compile to a single or only a few classes it could improve startup considerably.
Similar to that, I’d love to see dead code elimination, so if I only use 5 functions from core, I should only pay the cost of initializing those 5 core Vars, their metadata and their functions. That would also reduce startup time a lot.