Personally I think IJ4 will be more akin to IJ2, set in some part of the world no one knows (or cares) about, with a typical local evil dictator type trying to go for... whatever he goes for. Maybe it will be set in the Middle East, given the current hot topic of the day... maybe somewhere else. The Soviets, despite all the bad press and their actions, were not near as "evil" on the scale of Nazis.
Alternatively, it could be a rip on Da Vinci Code, or something like this... in which case it will get interesting. Having a conspiracy that controls just about everyone/everything be the villans... now that has the potential of matching up to the first three films. Have the Cold War be an invention of that conspiracy for whatever reason... have them be the people behind the Nazis, USSR, and some of the most idiotic WWII blunders (French strategy of doing nothing for a year, while Germany had a free hand, for one) - or whatever other conspiracy theory one can think of. The Illuminati, or the like, always make good villains