Nikas Kunitz
Warlord
First of all, I think Renaissance era free buildings should be changed to have jail instead of aqueduct. Aqueduct in general seems rather specific and advanced building to me, so having it as free building in this era seems a bit awkward to me. Having free jail will help greatly for expansion of colonial civs, by allowing founding more far away cities with decreased maintenance from the start. This purposefully includes Russia with its ostrog replacement for jail, allowing to found cities as quickly as you build settlers, without worrying about maintenance so much, while making them more productive from start. Free ostrogs and the UP I suggested are backbones of rapid and effective Russian expansion that it should have from its late 1472 start. Besides, I think most colonial settlements (not just Russian) had some sort of jail from their foundation (many colonies began as penal places in the first place), but nothing like aqueducts.l have suggestion about Russia's unique strength: new cities appear with a monastery and an ostrog. The reason is that removing the ostrog production bonus would critically complicate the colonization of Siberia, as each city requires the production of one settler, one or two workers, one or two strelets or crossbowmen, and one Orthodox missionary. Thus, colonization has a significant impact on the economy at first, and the central government did not strongly support Siberia's development for quite some time. Siberia's population was extremely small until the 20th century. For context, at the end of the 19th century, there was not a single city in Siberia larger than 100,000 residents.
Regarding the possibility of expanding cities to the 4th cultural ring, this removes the precondition for active development of Siberia in the 20th century, when technological advances and increased centralization of the state created the foundation for the development of eastern Russia.
Simply put, my proposal for a unique power is very similar to the Arab one, but the Arabs use it when capturing cities, while Russia uses it when founding them. It would also highlight the importance of the church in Russia before the 20th century.
Based on my experience playing Russia, to achieve a historical victory, Siberia needs to be colonized. However, the need to produce numerous units simply paralyzes the development of Western cities, and the increasing costs of maintaining cities and units are extremely slow to pay off, as Siberian cities require at least a monument or monastery and a catorga. As a result, the economy is simply paralyzed for 100 years.
The method of maximum historicism is impossible to apply, since the initial colonization of Siberia took place with very little government intervention, which is impossible to implement in the game without rewriting half the code.
I don't really understand how expanding to 4th cultural ring decreases need for development of Siberian cities as late as XXth century. Quite the opposite, UP I suggested is intended to quickly and widely expand cultural borders on mostly unimproved Siberian terrain, without need for additional cultural buildings, that will stay that way until XIX-XX centuries as it was in reality.
Secondly, I think we just should make newly founded cities to start with civ's state religion, maybe with some civic prerequisite. This is just more logical (settlers carry their religion with them, with some church often being the first "cultural building" they build in newly founded settlement) and should help with spreading religions faster and more realistic, especially in new overseas colonies (I noticed many/most cities in Americas often remain without any religion all the way into XIX century). This will save the time needed to build a missionary to spread religion to every newly founded city, making missionaries needed only to spread religion to other civs, that also can be seen as more realistic. Also, it will remove the minor "flavour" problem of some unrealistic religion randomly spreading to your newly founded city. In general, additional religions beside the state one should spread to larger cities, or be kept from before. Also, not directly about that, I think we need to do something with inquisition and autoremoving of religions, like Ottomans removing everything but Islam in Anatolia in Balkans, or Mughals removing Hinduism from all of India except the holy city.
As such, two of points of your suggested UP I consider worth adding as general features for all civs. Not denying its creativity, in my opinion it is a bit too specific (regarding the specific buildings and religion) and kinda generic as well, being crossover of Arabian and American (regarding what Dracoscolon suggested below) UPs.