OK so let me give some suggestions... 
First of all, on the steam workshop appeared Etruscan Civ mod which has LUA building which... adds culture and gold per city. And I am already working on reusing this wonderful code*
Maybe you wanna a piece of this Lua Cake? 
*- and I will struggle with it till making this lua working, at least for my own mods
Underlined parts mean I am not sure if it is possible to make them working or they seem to be difficult for me.
Arabian Madrasah - Doubled maintenance, +2 faith and instant Faith Boost after finishing construction.
+2 maintenance is for balance purposes, may also have increased building cost (this still makes historical sense because Madrasah is not some ugly school building but GLORIOUS MADRASAH
No idea how big this faith boost should be. On standard speed 150 faith?
Assyrian Karum - Karum - available on Currency. When built on City State territory connects its luxury and strategic resources
Karum - Assyrian trading outpost in far Anatolia. My idea was instant. Ancient and land version of Feitoria.
This is useful even during peace (remember my suggestion that each civ should have at least one non - warmongering bonus?
) but very helpful during early Assyrian warmongering. Although it seems to be particularly difficult as it requires Improvement 3d Model [eventually something like Kasbah can be used
] AND making AI civs able to use this feature...
Brazilian Sambadrome - replaces opera, 25% slower to build provides instant Golden Age Boost when built, when Sambadrome music slot is filled it provides +4 gold.
Version a) - instant golden age boost and +4 gold per slot filled. GA boost should be possible to code. Gold per slot filled can be easily created... basing on Paya from Burmese Civilisation Mod
Version b) - easier but more primitive - Sambadrome when built immediately makes empire enter short golden age (4 turns on standard).
Carthaginian Cothon - +5 to defense and +50% to building speed of Cargo Ships in that city
Current bonus is way too small. I have no idea how to code second part of this UB but it should be possible to do
Greek Agora - replaces Market, no +1 gold and 25% slower to build.
Increases Great People Generation by 25% and provides instant Culture boost when built. Boost increases for Each Greek City on map.
Easy to create.
American Whatever - replaces Bank or Stock Exchange, provides Instant Gold Boost
American Ranch - something like that http://steamcommunity.com/sharedfiles/filedetails/?id=165556849
Danish Viking Longhouse - replaces barracks, differences: +2 happiness and city immediately enters We Love the King Day. Viking Feast!!!
Korean Seowon - four science specialists instead of one. O_O Because, you know, it was SCHOOL, and also Korean civ specialises in science and education
Roman Forum - +x gold and culture per each city in the empire
Fits both Forum 'state' purpose and 'wide expansion' of Rome 
Netherland Waag - what do you mean by talking about 'resource traded in city'?
Mongolian Ger - current version but also bonus towards Production, so Mongolia won't be civilisation without peaceful unique feature
Babylonian - Ziggurat? Sumer Civ has the icon, we can invent new effect for it. For example: replaces temple but comes on Calendar and is faster to build, has scientist slot.
English Playhouse - current abilities.
I am not sure if each great writer increases GW costs in all cities or only in city with Writer's Guild... If it would break Playhouse, I would recommend changing Playhouse Writer slot into 'increases GW generation in city with Writers Guild/capital'.
French Salon - I would change great writers into great artists and provide great artist specialist slot
Mayan Holkan - maybe it will also provide... Golden Age Points when fighting?
Yeah I know that it will be fourth unit with this ability (after Minuteman, Pracinha and Clibanarii) but it still is much more original than Drill I
And fits Maya perfectly.
Turkish Bath
- Replaces Garden, doesn't require fresh water but costs 2 maintenance.
- ...I am sceptical about this Incense bonus because unique features which rely on single random luxury resource (out of 20) usually suck
and base entirely on luck. Maybe instead: +2 faith and PROVIDE Incense for city?
Shoshone Tipi - It definitely should have +2 food but I am not sure about +2 faith. It would be overpowered and Shoshone aren't famous for their religion
I would rather change it into +1 culture or gold. Available since Agriculture (?) and gold/culture bonus increases by 1 at Economics.
Venetian Canals - +2 venetian merchant points instead of +1?
Polish Uhlan - remember about changing its bonus towards MELEE towards GUN
Chinese Junk Ship - ...what are you planning to do with it?

First of all, on the steam workshop appeared Etruscan Civ mod which has LUA building which... adds culture and gold per city. And I am already working on reusing this wonderful code*


*- and I will struggle with it till making this lua working, at least for my own mods
Underlined parts mean I am not sure if it is possible to make them working or they seem to be difficult for me.
Arabian Madrasah - Doubled maintenance, +2 faith and instant Faith Boost after finishing construction.
Spoiler :
+2 maintenance is for balance purposes, may also have increased building cost (this still makes historical sense because Madrasah is not some ugly school building but GLORIOUS MADRASAH

No idea how big this faith boost should be. On standard speed 150 faith?
Assyrian Karum - Karum - available on Currency. When built on City State territory connects its luxury and strategic resources
Spoiler :
Karum - Assyrian trading outpost in far Anatolia. My idea was instant. Ancient and land version of Feitoria.
This is useful even during peace (remember my suggestion that each civ should have at least one non - warmongering bonus?


Brazilian Sambadrome - replaces opera, 25% slower to build provides instant Golden Age Boost when built, when Sambadrome music slot is filled it provides +4 gold.
Spoiler :
Version a) - instant golden age boost and +4 gold per slot filled. GA boost should be possible to code. Gold per slot filled can be easily created... basing on Paya from Burmese Civilisation Mod

Version b) - easier but more primitive - Sambadrome when built immediately makes empire enter short golden age (4 turns on standard).
Carthaginian Cothon - +5 to defense and +50% to building speed of Cargo Ships in that city
Spoiler :
Current bonus is way too small. I have no idea how to code second part of this UB but it should be possible to do

Greek Agora - replaces Market, no +1 gold and 25% slower to build.
Increases Great People Generation by 25% and provides instant Culture boost when built. Boost increases for Each Greek City on map.
Spoiler :
Easy to create.
American Whatever - replaces Bank or Stock Exchange, provides Instant Gold Boost
American Ranch - something like that http://steamcommunity.com/sharedfiles/filedetails/?id=165556849

Danish Viking Longhouse - replaces barracks, differences: +2 happiness and city immediately enters We Love the King Day. Viking Feast!!!
Korean Seowon - four science specialists instead of one. O_O Because, you know, it was SCHOOL, and also Korean civ specialises in science and education

Roman Forum - +x gold and culture per each city in the empire


Netherland Waag - what do you mean by talking about 'resource traded in city'?
Mongolian Ger - current version but also bonus towards Production, so Mongolia won't be civilisation without peaceful unique feature

Babylonian - Ziggurat? Sumer Civ has the icon, we can invent new effect for it. For example: replaces temple but comes on Calendar and is faster to build, has scientist slot.
English Playhouse - current abilities.
Spoiler :
I am not sure if each great writer increases GW costs in all cities or only in city with Writer's Guild... If it would break Playhouse, I would recommend changing Playhouse Writer slot into 'increases GW generation in city with Writers Guild/capital'.
French Salon - I would change great writers into great artists and provide great artist specialist slot

Mayan Holkan - maybe it will also provide... Golden Age Points when fighting?


Turkish Bath
- Replaces Garden, doesn't require fresh water but costs 2 maintenance.
- ...I am sceptical about this Incense bonus because unique features which rely on single random luxury resource (out of 20) usually suck

Shoshone Tipi - It definitely should have +2 food but I am not sure about +2 faith. It would be overpowered and Shoshone aren't famous for their religion

Venetian Canals - +2 venetian merchant points instead of +1?

Polish Uhlan - remember about changing its bonus towards MELEE towards GUN

Chinese Junk Ship - ...what are you planning to do with it?
