Wouldn't be hard to do. /pol/ already uses it. It will help with our discussions.
We have determined that flags will not benefit this board and will likely decrease the value of certain posters.
For example, guy who has lived in Japan for 5 years goes back home and replies in one of the many threads on Japan with an American flag next to his post would be considered a worse source of knowledge then someone who showed up in Japan a week ago but thinks they're an expert on everything Japanese and posts with a Japan flag.
Boards like /int/ and /pol/ where the majority of discussions are based on directly talking to people of either a specific country or many different countries are different from the type of discussion we have here. It's likely that flags would just add more trolling and shitposting instead of making any significant improvements to genuine travel topics.