>Ruby also has had far more success with JIT compilers than Python has.

Ruby is on its third (I think?) JIT now? I'm a little surprised, given Ruby's reputation as a wacky "anything goes" language with a very complex grammar, and it makes me wonder why that is? Does it have to do with the design of the runtime itself more than the language semantics? Or is it more incidental, e.g. many popular ibs are C wrappers, already generates bytecode files, and so on.

The difference is that Ruby follow the BDFL model, and Ruby's BDFL was willing to allow people to experiment with in-tree development of JITs.

If the Python steering committee isn't willing to do the same, they'll probably won't get a working JIT any time soon. Developing a JIT externally, or even from a branch, is just too hard.

Getting a JIT right is hard work because time spent by the JIT is time not spent doing actual work, and finding the correct tradeoffs is very much an empirical problem.