Per python/typing#516, it seems likely that we will have a choice between two ways to write type hints:

1. ndarray[Dtype, Shape]
2. ndarray[Shape, Dtype]

We'll probably have two generic arguments, but will have the freedom to choose in which order they appear. Do we have any reason to prefer one order over the other?

One weak argument in favor of [Shape, Dtype] is that it matches ndarray.__new__ (but that's so rarely used that it probably doesn't matter).