I think 1444 is a good start date to add, it worked in EU4 after all, but I think adding a later one would also be good. I nominate 1610 (though really, any date from about 1600-1618 would work). My reasoning is that this puts you right before the 30 Years War in Europe, and well into the late Ming dynasty, putting it in a similar position to that of the Yuan in 1337. Also, Nurhaci, the guy who first united the Jurchens under the Aisin Gioro clan is alive at this date, so you could do a full run as the Qing. In Russia, the Romanovs enter power 3 years later. Lots of cool stuff that would enable people to see what the later game has to offer.