Well right now Im working on a series of smaller Legends books (small in this case means about 80-100 pages each) detailing medieval Europe. These will likely be PDFs only, but depending on sales a print compilation is possible.
The first one is done is due any day, Legends of the Dark Ages, covering Europe from 476 to 814 (fall of Rome through death of Charlemagne).
Next will be Legends of the Middle Ages (Europe from 800-1300 or so).
These books are going to be smaller, mostly player material, because GMs already know how to capture the feel of medieval Europe, all the monsters in the PHB could conceivable appear, etc.
As for what's next in the major league way, meaning the full-on 80 page player's guide and 80 page GM's guide, followed by a HC print run, Id say China and Roma are probably the front runners there.
Chuck