Banking System, when?

A bank might get a bit complicated, I'd love to see personal funds be introduced aside from the house hold funds though. 

When you select a sim in the household, you'd see their personal funds listed under the household funds. When clicking on the personal funds you'd get a pop up where you can select which money they obtain goes into household funds. Like nothing, half their salary or all of it. Could also deposit a specific amount in there. Adults could also be able to withdraw a specific amount from the household funds to their personal funds. 

A system like this could also work with kids getting allowance, letting them negotiate for more and sims could also steal from other sims in the same household. In buy mode, you could switch between household funds and personal funds of sims. Sims could have an opinion again about purchases made as they did in earlier sims games, but now dependent on traits and who is paying for it. 

Like if you use the money of a child sim to purchase 

Would also allow sims to rent out a space to a house hold member, which would allow for so much more new ways to play a house hold. 

Also when a sim moves out, they'd be bringing along their personal funds instead of a roommate who never worked moving out and taking along half the money their friend with their good job made.