From time to time we revisit the list and consider adding additional countries to the whitelist, there's not much you can do from your side. The blocks are based on previous abuse history, meaning those that are blocked had a very high level of abusive users.
As far as I know there's no plans to revisit the list right now, it was recently opened up to allow more countries to sign up with our free hosting. There's no limits of this kind to premium hosting though, unless US sanctions would make it illegal for us to provide service to the country in question.
