I personally think a vector library that allowed some form of Einstein notation [1] would be a killer feature for a scientific computing environment.
https://github.com/mcabbott/Tullio.jl
https://github.com/Jutho/TensorOperations.jl
https://github.com/under-Peter/OMEinsum.jl
Tullio.jl is the most powerful and interesting to me of the above libraries, but they all have cool strengths.