My suggestion is simple: if you have enough stewardship (let's say 15) and you pick the "Amass a great wealth" ambition you would get an event chain to start earning money in alternate ways which aren't taxations or tolls. My thought is that there are no ways, in game, to represent some characters who got extremely wealthy even if they didn't have much land or a super castle: for instance, Lord Butterwell (the lord of cows), Lord Velaryon before the Dance of Dragons, Littlefinger, and others.
Ideally, there would be events about investments in activities tied either to the culture of the character, or his capital. Let's say for instance that you are a lord of the Riverlands and you start the event chain. You'd get events tied to the breeding of cows, for instance, or river trading. These events would in return give monye + perhaps either a character or province modifier to increase income.
What would be suited for each region, lore-wise:
Crownlands + Narrow Sea islands: Trading in the Narrow Sea (Velaryon), Moneylending in King's Landing.
Dorne: Wine, Building of canals, Growing fruits and products which cannot be found elsewhere on Westeros (Lemons, olives, and pomegranates), Desert Caravans.
Reach: Wine, Moneylending in Oldtown, Trading betwen Oldtown and the Arbor, Farming and making land estates more productive (the Reach has the biggest agricultural output)
Stormlands: No idea here. Agriculture, but perhaps for the Stormlands it should be more rare. It doesn't look like a particularly wealthy or economically rich region.
The Riverlands: Agriculture, Cow breeding (Lord Butterwell), River trading.
The Vale: Agriculture (Wheat, corn, barley and pumpkins), Sheep breeding (for wool), perhaps bee wax.
The North: the poorest kingdom in Westeros (with the exception of the Iron Islands), the events should be more rare for northmen. Timber, wool, furs and hides.
The Westerlands: it already has its mines, perhaps events could be about investing in existing mines, buying stakes and trying to find new veins.
The Iron Islands: nothing; they already have raiding and reaving.
Also, if one takes the ambition, has enough Stewardship and is either Ambitious, Greedy, perhaps Dishonorable, Deceitful or other similar traits there would be events about opening brothels (at the expense of prestige) and using other ruthless and dishonorable methods, regardless of culture or region (such as loansharking or exploiting winters and famines to make a profit). This should grant prestige penalties, though, and perhaps relation penalties with vassals and liege.
I've only spoke about Westeros since Essos has its republics and it has slave trading, but it could be expanded to the Free Cities as well (think for instance Illyrio becoming rich as a "cheese lord").
Tl;dr version: event chain tied to ambition (similar to the event chains to improve stats or to get a Valyrian sword) to earn money as a feudal lord and get rich without having badass land if you have the right stats and traits.
What do you think? Personally I don't think it would be too hard to script and it's totally doable with what we have. Doing events for each culture would be time consuming though, but it would be a great way to give more flavour to each region.
Ideally, there would be events about investments in activities tied either to the culture of the character, or his capital. Let's say for instance that you are a lord of the Riverlands and you start the event chain. You'd get events tied to the breeding of cows, for instance, or river trading. These events would in return give monye + perhaps either a character or province modifier to increase income.
What would be suited for each region, lore-wise:
Crownlands + Narrow Sea islands: Trading in the Narrow Sea (Velaryon), Moneylending in King's Landing.
Dorne: Wine, Building of canals, Growing fruits and products which cannot be found elsewhere on Westeros (Lemons, olives, and pomegranates), Desert Caravans.
Reach: Wine, Moneylending in Oldtown, Trading betwen Oldtown and the Arbor, Farming and making land estates more productive (the Reach has the biggest agricultural output)
Stormlands: No idea here. Agriculture, but perhaps for the Stormlands it should be more rare. It doesn't look like a particularly wealthy or economically rich region.
The Riverlands: Agriculture, Cow breeding (Lord Butterwell), River trading.
The Vale: Agriculture (Wheat, corn, barley and pumpkins), Sheep breeding (for wool), perhaps bee wax.
The North: the poorest kingdom in Westeros (with the exception of the Iron Islands), the events should be more rare for northmen. Timber, wool, furs and hides.
The Westerlands: it already has its mines, perhaps events could be about investing in existing mines, buying stakes and trying to find new veins.
The Iron Islands: nothing; they already have raiding and reaving.
Also, if one takes the ambition, has enough Stewardship and is either Ambitious, Greedy, perhaps Dishonorable, Deceitful or other similar traits there would be events about opening brothels (at the expense of prestige) and using other ruthless and dishonorable methods, regardless of culture or region (such as loansharking or exploiting winters and famines to make a profit). This should grant prestige penalties, though, and perhaps relation penalties with vassals and liege.
I've only spoke about Westeros since Essos has its republics and it has slave trading, but it could be expanded to the Free Cities as well (think for instance Illyrio becoming rich as a "cheese lord").
Tl;dr version: event chain tied to ambition (similar to the event chains to improve stats or to get a Valyrian sword) to earn money as a feudal lord and get rich without having badass land if you have the right stats and traits.
What do you think? Personally I don't think it would be too hard to script and it's totally doable with what we have. Doing events for each culture would be time consuming though, but it would be a great way to give more flavour to each region.