Seeing as they only release titles that add up to 9 I kinda knew they would be stepping back in time. A super futuristic title of for example 3600 would have been difficult to conceive!
There's a few numbers they could have gone with for further futuristic Anno games; 2520 and 2700 being two possibles. They may do something futuristic again after 1800, as that will be the fifth game set in the past and two that have been set in the future.
I wonder, if there were ever to be a 9000, what that would be like.