So I consider a new one to company with it.
Maybe all techs (excluding advancing ages, castle techs and monastery techs) cost -50% gold.
Btw I’d like to add a new effect to Tsikhe, barrack units and archery range units can be trained at Towers. I think it could make this UT more flexible and give an interesting strategy to their late game tower rush.

Will be good as a DLC with rename/rework Slav to Rus
I remember a rumor that there was a big DLC with Armenians, Georgians, Vlachs, and Russ renamed from Slavs. If the dev want to finish Europe with a big DLC like the last one, it will be fine.
Btw, about the Vlachs, I had putted forward an idea about “Țintaşi”, the Vlach marksmen, as their UU before.
Low HP glass cannon, able to be a charged shot much like the coustillier. On the other hand, for reflecting the ambush, the attack from Țintaşi may not show their location automatically if they are out of your LoS.
Some people always think that the UU of the Vlachs/Wallachians has to be cavalry, which makes me find it boring. There are only 5 foot archer UUs in the game, I hope there could be more.
No matter Vlach should be introduced or not, some your arguments may seem imprecise. For someone, the area was already covered by Magyars, Slavs Byzantines and Turks in AoFE. Bulgarians? Slavs. Cumans? Magyars. Tatars? Turks. Even Goths might cover Magyars and Slavs well in AoC for someone who cared nothing about European history. It depends on how you define the word “cover” so this argument is imprecise. What did Vietnamese achieve? Conquered by the Chinese for the thousand years? What …