What do changes in Pakistan's nuclear program mean?

A recent Washington Post article reported Pakistan’s construction of a facility to produce plutonium, rather than uranium, for its nuclear arsenal.  The Ploughshares-funded Institute for Science and International Security later issued a statement on the Post’s description of Pakistan as having a “more mature program,” saying the term implies “that more destructive nuclear weapons somehow lead to a better nation.”  ISIS continues that the word choice distorts the debate as Pakistan seeks “to turn the public debate over its nuclear program into a binary choice between Pakistan expanding its program and Pakistan modernizing its program.”

ISIS writes, “‘Modernizing’ a nuclear weapons program, rather, should at most be interpreted as improving the security of existing nuclear weapons, increasing security of fissile material in storage, at military and civilian nuclear industrial sites, or in transit.”