They could add variants of the Gaelic helmet for Battania and variants of the burgh helmet for the empire.
Add other Pavise shield designs
I think they could also add a shoulder mail of a darker color to match the other vlandia chainmail armor.
Vlandian champion horse armor could wear tabard with our banner
Finally it would be great if the swadian knight skin was recovered and used in the vlandia banner knight and equipt with a great lance
I know it does not match the period, but as Vlandia is on the side of the empire it would not be strange that the wealthiest knights could afford a plate armor similar to the cataphracts of the empire.