Apparently there are reports of people being banned for playing it in unsupported countries, but I can't find any hard evidence of this. Articles say it's happened, and to be cautious, but the closest thing to hard evidence is a screen cap of the "servers are busy" screen. If someone is actually banned, and there's a "you are banned" screen, why aren't they showing it? I have suspicions that anyone has actually been banned.
It'd be really easy for niantic to just ban everyone outside their currently active countries all at once, there's no point to doing them as one-offs.