I was wondering about doing this originally, and then i just kind of never did... and then i forgot about it.
I might well add this in the next update as well - you are really good at these suggestions.
One problem is how to distribute the pollution - a big blob at the centre would be easy enough, but not as realistic - another way would be to just do have t drop off as you get further from the nuke. A really cool way would be to use NukeMap to create a more accurate simulation - at least of the core impact, and possibly use the in game wind to find the cloud fallout as well (which is any radiation dropped from the cloud formed by the weapon).
I'll look into doing something more detailed with it, or might just take the lazy option... I'll have to see - it would be cool to see the pollution spreading downwind of the nuke.