Rulers should be able to actively invest money in businesses

There's also a mod that has a GoT compatable form called the Great Trade League that allows you(Or a courtier representing you) to enter an international association of merchants money lenders and the like. It allows collecting resources, finding exploitable things like mines and flax fields, buying and trading both raw goods such as iron and grain and refined goods such as weapons and booze. You can deploy these into specific provinces by "Selling them on the market" for various bonuses like decrease build cost for lumber and stone or increased army moral for alcohol. You can also hire associated craftsmen to refine goods up the chain and expand profits, plus in war can economically attack provinces of people with your influence. Think in more recent versions there's even the potential for fuedal lords to band together in an economic war with the great trade league dumping money and manpower into wresting back control of their local economy.

But not sure that would be quite what your looking for. It also sometimes causes random MRs to appear since one of the upper level powers potentially allows you to convert yourself to an MR from fuedal.