Is it possible, to introduce grand Duchy of Lithuania in the late campaign? There is plenty of units now : Lituanian troop, Baltic troops and militia from Rus duchies. Historically, in XIV Century Lithuania expanded rapidly, acquiring lot of lands from the weakened Golden Horde. Sometimes they acted as sort of military protectors slash bullies. They got quiet big, controlling modern Bielorussia, Rus lands such as Smolensk, most of Ukraine including Kiev, reaching as far as Black Sea. And later they got the union with Poland, i dunno shall it be included in the mod.

Introducing Lithuania would be beneficial both historical and good balance wise. For example the Teutonic Order fought mainly against Lithuania back then. Eventually, Lithuanians sealed the lasting union with Poland, i dunno if it should it included in the mod.

I would also introduce Muscovy in the late Campaign, perhaps as allies/tributaries of the Golden Horde. Muscovy started it's geopolitical carrier as Mongol tribute collectors. And it was them, not the Novogrod, who got big.

Right now the North Eastern theatre of war feels bit barren comparing to Iberian Penisula and Caucasus.