I have been putting together a Byzantine Mod based on a request I received and my own interest. This mod comes in 2 flavors: Ambition (1071 borders) and Last Stand (early 1453 borders). This mod still needs some of the details worked out, such as names, policies, and leader stats. The smaller mod assumes that the Byzantine Empire last a few more day before destruction while the larger roughly re-established the 1071 border (per request) and eliminates the Ottomans.
I will be releasing the beta momentarily for playtesting, all I ask in return is input and criticisms. Remember, this was done in one seven hour stretch so far, so it's definitely a work in progress. To play as Byzantines, you MUST start on May 30, 1453.