I don't think a bank would be the best add-on but individual accounts would be nice. When teens are working as babysitters or a barista, it would be great for them to have their own bank account. What for? So they can go to the mall and buy things or for the bar (which I am still fathomed that my teen Sims can order drinks at the bar/nightclub). I also wish that these jobs for the teens were available for adults like in past Sims games. Do all the adult Sims need a career type job? Can't they be a nanny/housekeeper, barista etc too?
I do agree that it would be great to have a mortgage system where the Sims could still pay full price for the house up front as we do now or they could submit payments like the Apartment life expansion. Most of the time my Sims only start with a small amount of money and I have to move them into an empty lot, use the motherlode cheat to increase their balance and then move them again into a built home. It would be great for the Sim family to purchase any home they would like and pay a mortgage or something similar like with the bill pay system. They could set it up like how the bills are in the Sims 4 where if you don't pay in X hours per Sim week, you'll lose your lights etc.
Open for Business was my favorite expansion of all time and I've owned all of them at one point or another. I loved that the Sims could either start a business on their own lot, like a florist shop, or have a lot in town for their shop/restaurant. I even once built a mall where the full Sim family of 8 ran every shop in the mall to include the restaurant. I also loved having a grocery shop as well. I miss the little shops like that in town where a Sim could buy a dozen roses from the florist, a nice cake or cupcakes from the bakery and swing by to pick up groceries from the grocery store. I spent so much more time playing that expansion then anything else. I am very hopeful for a similar expansion for the Sims 4.
