Selective Nuclear Proliferation sorry to say it is a Pandora box can worm BS. It is just openly say the standard for Proliferation now open to everyone interpretation. Why only Western powers or Allies that can have it ? Who or what power that say that one can have it, the other one can not. Only US allies can have it ? That:s big BS for the rest of world.
Let's example Middle East, it is already tough US handling at this moment to hold Saudi and Egypt back from acquiring Nuclear capabilities because Israel have ones, and Iran closing the gap on every opportunity. The moment some Western nations in Europe or North America fell they should have it, cause they disappointed with US, then Middle East will say, well if those Western nations think it is alright to have ones, we will not be following some 'hypocrite' standard to have our own.
How about Asia, the moment ROK and Japan see the selective Proliferation can be word out, then they will use North Korea arguments. Then ASEAN especially Indonesia feel the can of worm already open, let's have it. Do you think Australia will stay silence ?
Current Proliferation regime is not perfect, but it is still better then alternative. Selective Proliferation is bad idea, cause it is simply can lead to everyone have their own arguments to developed their own Nuclear armament options. This is not 60's-70's anymore. Building nuclear capabilities is not an unachievable tech anymore for more nations. Like it or not the Non-Proliferation strangle from the Big 5 still the best option for World Order. Opening that limitation, is opening chaos and not order.