I don't have much to contribute except "I agree".

I'm a "small" maintainer here, I'm mostly answering question and merging small PRs. I know ndarray as a programmer, not as a maintainer. In brief, I don't know much about the internals. I do know about the Ix# "hack". If ndarray was coded today, it would probably use something else!

Because writing generic functions in Rust is "ugly", I tend to choose a float type and stick with it. Later, I realize that I also need the other float type so I make it generic over num_traits types. Slightly related, I wrote this function for another project that I maintain. It's ... not sexy. I don't really want to be writing that kind of code. I was a C++ programmer a while ago and I did like the freedom to write generic code in that langage. (I still prefer Rust)