hmm, from my point of view, your third point is a bit strange, since its the threat from other nations that encourages diplomatic engagement. So to use an example the spectre of Xinjiang led to people talking to eachother to find ways of putting Mr George in his place or the threat of Romnesian dominance (and the knowledge he could hurt us) led to nations working together to bring P_F down a notch.
If you remove the threat other players represent however (which is precisely what universal nuclear weapons is) the result is glorious isolationism. Afterall if, as you say, direct war between major powers is all but impossible because one is secure in ones ICBM ringed fortress, there is no imperative to talk to people at all since you can just go about your business with the minor powers completely secure that you can ultimately get away with it scott free.
Thats why I would actually support no WMD's at all. In that case the threat of other players remains, and war would also be more interesting because players just can't be instantly wiped off the map.