That's a very interesting post you linked Perkus. I'll start thinking about all the problems in that list.
Something I've learned when it comes to balance is that if there's a bunch of factors all contributing to 1 problem, attacking those small things can solve even totally unrelated issues. For example, the overpowered state of Horsemen in vanilla is due to a combination of horsemen strength, weak ai, open/rough terrain ratio, late reveal of Iron, weakness of alternate units, resource abundance, etc... many factors.
Any superiority of ICS over "normal" sparse development could be considered a core game problem like the ignore-happiness exploit, so it's something I'd rather leave to the developers to solve on the whole, but I can fiddle with all the little factors that contribute to it. Something that would be in the realm of this specific mod is the underwhelming nature of National Wonders. Improving them will also help expansion vs small empire balance issues.
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Here's some things I'm working on.
Been considering a buff to these for a while now. Improving National Wonders would be helpful for general expansion vs small empire balance in general, not just ICS. One idea I've had is adding more specialist slots to these buildings, giving small empires extra specialist and GP potential.
Something like...
National Epic: 2 Artists and +50%

(double)
Hermitage: 2 Artists
Heroic Epic: 2 Engineers
Ironworks: 2 Engineers and +40%

(double)
National College: 2 Scientists
Oxford University: 2 Scientists
<something famous>: 4 Merchants, requires <some weak building>
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Aqueduct
+25% city growth rate
Construction tech
(Hospital effect and cost halved)
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Baths of Trajan
Requires Aqueducts in every city.
+10
Massive bathing and leisure complex built in Rome from 104-109 CE. Purpose of this National Wonder will be dealing with one aspect of ICS. Colosseums will have -1

, yet a small empire with this National Wonder will have equal or greater happiness than vanilla.
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Agra Fort
Requires Castles in every city.
+50% city hitpoints.
2

Merchant slots.
This is a famous walled city in India, capital of the Mughal empire in the 16th century CE, and housed a gigantic treasury and mint.
Increasing hitpoints with a building is not possible yet, so as a temporary measure I'll give the same strength bonus as a Castle or something.
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Medici Bank
Requires Banks in every city.
+50%

2

Merchant slots.
A financial institution created by the Medici family in Italy during the 15th century. It was the largest and most respected bank in Europe during its prime. This is again to work in with ICS migitation.
Thalassicus said:
The Medici Bank would probably be joined by a slight reduction to normal bank and/or market yields. Overall there would be more gold for small empires but less gold for large ones, similar to the concept for Baths of Trajan, to make small empires and national wonders a more worthwhile strategy.
For example, if Markets produce +20% gold (down from 25) then with this +50% wonder your empire would have more gold than vanilla when smaller than about 10 cities, and less gold when over 10. (50 / 5)
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I haven't done art yet for CiV... so I'll have to learn how to go from Photoshop images to CiV icons. Probably will have placeholder icons to start.