That's certainly one way to get people back into MGS V, especially with all the Fallout 4 excitement starting to dissipate (albeit slowly). Not only is the event divided by region, but platform as well. So it's co-operative and competitive at the same time.
All the details are up on Konami's website, but here's the important bit:
There is another important secret in Metal Gear Solid V: a hidden event that can only be unlocked when very specific conditions are fulfilled.
1. You must have completed Mission 31. 2. You must not own or be currently developing a nuclear weapon. If you have any nukes in stock, you must dismantle them. 3. Certain conditions related to nuclear proliferation must be met on the regional server for your corresponding gaming platform (PlayStation®4, PlayStation®3, Xbox One, Xbox 360®, PC(Steam®)). 4. All nuclear weapons on the regional server corresponding to your console or platform must have been dismantled. In other words, the amount of nukes on your platform's server must be equal to 0.
And what happens when you satisfy these? Well, that's the secret:
If all four conditions are met, you will automatically trigger the secret nuclear disarmament event when you return to Mother Base or after you complete a main mission. Should new nukes be developed after conditions 3 and 4 have been fulfilled, this event can be repeated by fulfilling all four conditions again.
We will be updating the amount of nuclear weapons owned per platform regularly through our official twitter accounts.
This is Konami's Twitter account, with the latest platform numbers (27 November) below:
Here are the numbers for nuclear weapons owned per platform. By Nov 26th- PS4：349、PS3：215、One：81、360：75、Steam：15206
— METAL GEAR OFFICIAL (@metalgear_en) November 27, 2015
So time to get dismantling I guess... if you're not to busy roaming the wasteland (or going by Steam's current top sellers, running people over or stealing cars).