Julia is there now. It seems absurd to me to build this on top of Python. You are building everything as a DSL that needs to be carefully crafted to never touch the data structures of the host language. Changing from Python to Julia and suddenly being able to use datastructures other than numpy arrays, and writing things that should be for loops as for loops, was such a relieve. But, I guess as Javascript has shown, with an infinite amount of engineering resources dedicated to it you can build anything in any language.