The trade-offs between a single JITed language versus having a scripting and native language are interesting. I think there are a few advantages to the latter a

The trade-offs between a single JITed language versus having a scripting and native language are interesting. I think there are a few advantages to the latter approach though. JIT is never going to beat carefully hand-optimized code, and the amount of code that needs such optimization is small. Furthermore the performance of JIT is not necessarily predictable, and comes with additional memory usage. Finally languages such as Python, R, or Matlab have a vast ecosystem of libraries; this gives a big incentive to keep on interoperating with them instead of switching to a new language.