Interfaces to HDFS how? PyObject has to get translated somewhere.

Arrays of custom element types is a good first start, but boy is dynd a seriously overengineered way to accomplish that. I'm referring to array structure, sparsity, symmetry, linear algebraic properties that should be reflected in the type system. Python's type system is lousy for this, and C++ isn't extensible.

Julia can fix performance on heterogeneous data with gradual compiler improvements, and the string representation is due for a major rework. Python can't fix the fact that the language and libraries were not designed to be efficiently JITted, and extension interfaces are closely coupled to the CPython interpreter's API.