If you're willing to let go of imperative syntax, Interaction Nets[0] might be interesting to maximize parallelism where possible. I think Bend[1] is probably the most mature implementation of that idea.
From what I understand, Julia doesn’t do any tracing at all, it just compiles each function based on the types it receives. Obviously Python doesn’t have multiple dispatch, but that actually might make compilation easier. Swap out the LLVM step with python's IR and they could probably expect a pretty substantial performance improvement. That said I don’t know anything about compilers, I just use both Python and Julia.
