If I could give this idea a -2 I would.
Identifying the poster's nationality would hinder the discussion of ideas.
Although it would be nice to know more about any given poster as a person, I think that our prejudices about the poster's nationality will intefere with our analysis of the poster's arguments and ideas.
The whole beauty of K5 is that we can disregard borders and all that other stuff when we talk about ideas.
Compare K5 to BBC's "Talking Point". BBC is obsessed with nationality; you must tell them your nationality before you post, and every poster is identified by name and nationality. Is nationality really that important? I don't think it is. Worse, there are many people out there who will give posters high or low ratings solely on the criterion of nationality. It already happens a lot in the various "US versus Canada" discussions.
People get funny when they get nationalistic. When K5 brings in nationality icons people will instantly abuse that system. Imagine the fun the trolls would have...
Usually if nationality is important enough to mention, it'll be mentioned.