I just don't see Go ever becoming a good language for numerical computing. There was such a push with implementing [multidimensional arrays in Go](https://github.com/golang/go/issues/6282) but it looks like it's been shot down more than once.
When using Python and R interactively, the syntactic sugar and functions that allow for rapid analysis (subsetting, indexing, merging data objects etc etc) more than make up for the slowness of the language. If someone wanted to implement that workflow in Go for repeated analysis of very large datasets, I doubt they would need it to be interactive.
But it looks like Julia might become the goto numerical language that is compiled and fast.