What would you propose as the win conditions for an Economic Victory?
It can be archived in various ways. Let's take this scratch as an example.
Aim: to dominate markets.
1. The value of the market is a sum of gold income generated by all Civilizations throughout the game, so it will increase turn by turn. So we have a bunny to chase now.
2. How we can chase that bunny and what will be our offensive currency. Let's use the Corporations mode idea of products. Each product manufactured by your Civilization will have a gold value.
3. To dominate the world market and claim economic victory you must earn the sum of the gold value of all your products earned throughout the game larger than 50% of the current value of the World Market.
So now we have basics with a good story. Domination of world markets It means you must produce over 50% of goods that the world is able to buy. in general monopolize the World Market. Sounds like a good reflection of the real-life economy in a game.
And now the twists and modifiers to spice up the game.
1. Defensive (producing more gold, increasing the value of the world market by policies, buildings, Wonders, trade routes, spies, World Congress resolutions, decreasing value of the Civ's products, etc.)
2. Offensive (produce more products, increasing the value of your products by policies, buildings, Wonders, trade routes, spies, World Congres resolutions, decreasing value of the World Market, etc.)
Additional features:
1. Unique Products for Civs.
2. World market - you can choose to either put a product in your Civilization's building (local market) and earn its benefits and buffs or put a product in a World Market to dominate the world market (Only sum of the value of products put ina global market would count for Economic Victory in this case) and win an Economic Victory. This way products will be usefull not only in economic game but also support different win conditions.