I think the part about the kilogram is missing the point -- it's not that a pure silicon crystal sphere is a better artifact to be the kilogram than the platinu

I think the part about the kilogram is missing the point -- it's not that a pure silicon crystal sphere is a better artifact to be the kilogram than the platinum-iridium cylinder. The idea is that they are defining a reproducible process to manufacture an object of known mass without reference to some artifact at all. They are proving by demonstration that anyone can manufacture such an object and then test it for chemical purity, perfection of crystal lattice, size, and sphericity. This allows you to form a counting argument based only on math and the physical laws of the universe that the produced object has within some small error exactly n silicon atoms in it, which will then be the definition of the mass unit (any sphere of n silicon atoms, not any particular one).