There exists a much smaller subset of jank that is capable of compiling itself. I am quite sure that you could write a bootstrap compiler in clojure (but restricted to the same subset) that translates to clojure (or some other language you prefer targeting). My guess, from experience writing small compilers, is it should be doable in ~5000 lines or even less.
Once you had that, you could then write a backend that translates to c. This gives you a native compiler for this small subset of jank. Applied to its own source code, you get a native compiler binary for free and cut the cord from clojure.
Now you have a native compiler and a very small, tight language. Because it is so small, it is easy both to check correctness and optimize. You can add new backends relatively easily. For the repl, you can compile functions into their own hash-addressed shared libraries using a c compiler and dlopen them. TCC is very fast for this purpose even if the generated code isn't quite as good as optimized gcc or clang.
All of the future vision could be implemented on top of this foundation. The current approach is likely going to just bog the author down, dealing with accidental complexity from c++ and llvm especially. It is also better to have fewer features implemented completely and correctly than more features incompletely or incorrectly implemented.