Since the announced DLC never existed, here is my 2023 idea of what the Poles could have looked like:
And as a bonus, my old Kazakh civ idea that I had posted on this forum.
I’m now developing my own game greatly inspired on AoE3, that includes many of the elements from these two suggestions.
AoE3 will always remain a great source of inspiration and a paragon of RTS, one of the very few ones which are set in that era.