I’ve seen that about 67% of all isk is in the hands of the top 5% of the players. Unlike in real life however, this isk is not invested in any way, just sits on the bank accounts. That amount of isk can be considered “lost” from the game’s perspective.
First of all, I think it would make sense to allow these people to invest or lend their money (and helped in this with a feature so they won’t be scammed to poverty), for instance to buy NPC shares or shares in any corps (which are set to publicly traded). They would get some dividend, sell shares, etc. And they would be able to lend money for a small margin to other players, thus giving a boost to the economy.
There could be lot’s of ways to provide money for the NPC corps, they would gain capital from the sales taxes, there could be property taxes paid to the empires the player started in (maybe some option to change your nationality if you would like to boost Caldari instead of your initial Gallente or something). There can be a small docking fee for unpacked ships/stations depending on size or even a smaller fee for any tons of storage space you use in a station. Maybe only some maintenance costs for your ship, that is for CCP to decide.
But why would that be beneficial? Right now the NPC side of the economy is an infinite sink (sales tax) and infinite sources (missioning, bounties) not dependent of each other. It is modelled so. There are other sinks and sources (like rat items, destruction of ships, mining, exploration) that are somewhat more balanced by each other, but isk is pretty much ever-growing like it is printed (and hence, inflation). Mining could be an issue but since blown up ships don’t give minerals and ores, it is fine. I think it would make a good simulation if there would be the NPC side of the economy implemented too. Although a little money printing wouldn’t be bad thing, especially if the player base changes upwards (so the minimum total amount of money could really be dependent on the player count).
For instance, if a corp, like Caldari Navy has lot’s of mission runners, they would decrease their reward for missions representing an overstimulation of capsuleers they can hire. Also if their capital is shrinking they would be able to provide less money. That capital would be replenished by the income of the corporation. Rich corporations would pay even more. Also, bounties could be payed by concord, the mission giver or in case of belts, anomalies and normal space, every corp that is in the system equally, and they can “dry out” (lessen) too for a given system. That would make some shifting between where people mission etc and what they do, and the game would be a bit less static. Also, there wouldn’t be “exploited” systems or corps, where you just gather (mission) but don’t give (sell, invest, etc).
These alterations and implementations would greatly change the game in an interesting direction even without implementing the other parts of the NPC economy (like npc production of goods beyond what is now rat items, which can be considered as npc industry).