It’s not out of the question that additional `Index` impls for other integer types could be added to the standard library at some point; the issue is discussed

It’s not out of the question that additional `Index` impls for other integer types could be added to the standard library at some point; the issue is discussed often enough. But it’s not trivial to do because some currently valid code could become ambiguous if impls are added, so some sort of a transition would be required.