Nuclear weapons can not be uninvented, nor are nation-states willing to allow deeply intrusive inspections or grant the U.N. Security Council authority to take preemptive action against nuclear proliferators. Nothing less than such radical steps would make the elimination of nuclear weapons plausible. But neither does the nuclear status quo make sense. For at least the next generation, the nuclear agenda should focus not on abolition, but on tighter controls of nuclear material, which is the major obstacle for nuclear wannabes. There are various degrees of de-alerting that could be negotiated, effectively expanding the time required to launch weapons to hours, days, or even weeks.
Numbers are less important than removing nuclear weapons from hair-trigger status.
The point of arms control is to increase stability and reduce the risk of war. Less is not necessarily safer. If China builds up while the other declared nuclear weapons powers build down that could be destabilizing. But if this is the case, it would be in the best interests of the United States and Russia to consider shrinking their arsenals to a level anywhere between a few hundred to one thousand. As a matter of principle, if adequate verification and enforcement against nuclear breakout were possible, a zero nuclear option could be obtainable.