They should make it so you can invest in things. Like pay 30,000 gold to upgrade a towns guard from light armor to medium or heavy armor. Or pay to clean up a city, train a militia or something. The reason why I say this is because half way through Oblivion I had so much gold and nothing to use it on, it just got really boring.

you can invest in traders in Oblivion

invest in stores or new mining operations in diffrent parts of skyrim previously not mined. also you could start your own store

You could buy mushrooms. You know, make potions and stuff.

To be honest, I never once used a trader in Oblivion. They scam the hell out of you. You know you're not going to make your 500 gold back. I ended up dumping all my loot in the lobby of the Arcane University.

As for investments, it is something that would be interesting. You must know what comes next though... "It's not that hard to do in a mod"

1. Add dialogue to a person, maybe a rumor/clue to another2. Create script to replace armor in form lists that is activated by the dialogue

Or like in the Bloodmoon expansion for Morrowind when you invested and built that little town "Raven Rock," I think is what it was called.

Exactly

Wut? You're kidding, right? Merchants typically have no more than 800-1000 gold. If you give them 500, they suddenly have 500 more for each item you sell . Daedric items and such are typically worth much more than any merchant will pay for it, but if you invest in their store, you will get a higher price for your items and will make that money up in no time.
Not saying that system is great - only saying you're wrong

well you know you give them that money so they have more to buy from you, I usually get a bunch of armor from rockmilk cave