I think there should be some sort of treaty you could sign with different countries that limit or ban the use of nukes, and I guess if you break the treaty everyone gets really mad and probably declares war on you. Also you should gradually be able to build more and more powerful nukes as research continues that would destory cities with higher populations, a standard nuke would destroy all cities under 6 pop., while a more powerful nuke would destroy a city with under 8 pop, that sort of thing. A larger damage radius and increased fallout would also result.
And I guess maybe whoever has the currently most powerful nuke or nuclear stockpile would definitely be on the minds of other civs, unless a treaty has been signed delcaring you won't use them.
Just my ideas.