User blog comment:Master Sima Yi/Assassinews 12-05-'15 — Assassin's Creed: Syndicate has been revealed!/@comment-210.187.170.102-20150810070759/@comment-24760042-20150810144442

They are running out of historical and people eras which the mass audience can identify with, and it seems these are the type of games AC like doing best. They leave the lesser known events to comic books and spin off games.

The only two eras I can think of are the American Civil War and Feudal Japan as they are not too far into the modern era as well. If the AC Team are willing to go before the Hassan-Altair era this will no longer be a problem as there are many more to explore.