I agree with you justhuman, China would logically be the next choice of 'King of the North'.
It's still a communist country as was the old king of the north. It has the largest army, fastest growing economy (6th largest in the world), it's on the UN security council, and who knows what arguments will develop between the US and China as manufacturing jobs go from one to the other.
I suppose Islam could be a choice because of the present conflict. I just had a quick glance at my 'Pay Attention to Daniel's Drivel' book and it says the Soviet Communist bloc replaced Germany as 'king of the north' simply because it stood 'in strong opposition to the Anglo-American alliance'. So I suppose using that line of 'reasoning' then Islam would now be King of the North. I don't think the Watchtower will actually state this but may say something like 'time will tell' if Islam has become this King.
It would save them a lot of time and effort if they realised the real King of the North died over 2000 years ago.