Just finished looking through the entire OP. Here are my thoughts on some of the things that stuck out to me, but this of course isn't exhaustive:
America - Trailblazer: There's been a lot of discussion concerning this UU, but as it's described in the OP right now it's just laughably overpowered. A pathfinder replacement that can settle with any buildings researched pre-built? That's a settler with free buildings that you get to build before you have researched ACTUAL SETTLERS, that get free monuments, minimum. That is completely absurd. Regardless, with the Ranch already slated as the civilian UU/UI/UB, you should be looking for a military UU anyways. ie.
Nimitz carriers,
Rough Riders,
Monitor, etc.
Brazil - Samba School: With the latest era UU proposed already (Pracinha), having the latest era UB too is pretty damn crazy. That being said, the bonuses as presented right now are crazy game-ending hilariousness. It makes Brazil's playstyle just "survive", and I think that's pretty funny, especially given it's real-world position as the 'next rising power' for..... about 40 years now. Lol.
Byzantium - Hippodrome: absolutely required. Full stop. I know people were saying events/choices=bad, but there should be a prompt asking people to decide whether they support the Blues or the Greens. Nothing happens, but maybe there's a notification every so often that a riot happened at the hippodrome...
again
Denmark - Ting: This building strikes me as having virtually nothing to do with Denmark's playstyle. imo they should get a mead hall replacement for the Garden. +food, +GP production, reduce boredom slightly.
Carthage - Shofet - Nothing bad to say, but I am pretty on the fence as to whether a unique general constitutes a unique civilian unit, and therefore isn't up-ending the civilian/military balance? Also, I was hoping to modify the Israel mod and make the Shofet their unique; so much for
that. 
Carthage - Numidian Cavalry - Why was this chosen over simply giving Carthage access to a war elephant that doesn't require ivory? The Carthaginian war elephants are way more iconic.
Egypt - Khopesh - unusual weapon seems like a strange choice. Khopeshi aren't really that strange; they aren't
Shotel. imo they should get a promotion increasing their CS on attack, to reflect that Khopesh are effectively battle axes when used correctly. Their sickle blades are highly effective against unarmoured or lightly armoured adversaries, so maybe a +cs vs enemies with lower base CS (ie<15?)
Germany - Jaeger - When I first saw this I laughed, and hoped someone had actually proposed a GDR replacement, lol
Korea - Turtle Ship - I'm surprised you landed on Galleas as the replacement. Turtle ships were often used to ram other ships and fire broadsides at less than 20m. A caravel replacement seems much more appropriate. Also the Turtle ship's name in Korean is Geobukseon
Morocco - Menara Garden - in the state it is proposed in it is just way too weak and situational
Songhai - As the OP is now, the UU is completely missing. I'm guessing the
Sofa is supposed to be there from the rest of the discussion?
Aztec - Eagle: As it is described in the OP, it actually sounds like a downgrade from the unit it replaces. Why not take a queue from civ VI and have the unit spawn a worker at the nearest owned city if it kills a unit? This reflects the Eagle warrior's famed ability to capture enemies in battle. Also could we change the name to cuāuhtli? Thats the proper name in Nahuatl
Celts - Oppidum: This looks to be about as good or better than a great person tile. In fact, Oppidum are essentially towns, so why not actually make this a UI replacement for towns, and add +3 great merchant points to all the Celtic pantheons?
Maya - Ball court: I'm not really a fan of adding happiness to UBs that aren't Persian Satrapys; That's kind of their jam. I'd reduce religious unrest or crime in addition to the arena's reduction in boredom. Otherwise, make the happiness conditional on city connections or something. The ball courts were often used in Mayan culture as a form of conflict resolution between squabbling city-states and nobility.
Lastly, okay, there is a SERIOUS lack of consistency on whether culturally relevant names are used or anglicized versions. Why refuse to call the ball court a
pitz court, and yet call a stave church '
Stavkyrka'?