A game where you run a realistic organised crime group. No romanticised noire stuff. In a modern-day city, trying to make money doing various illegal activities, then doing as you please with it. Possibly with a variety of settings to play your campaign in (e.g. Industrial city, large commercial services-based city, squatter settlement, etc). I think it could be pretty good, as long as it doesn't get people ranting at it because moral reasons. Which it inevitably would.
I actually had an idea for something like that a while ago, but instead of modern day it would be more Prohibition era. Like, you'd have to maintain speakeasies and whatnot.
Another game I'd like to see is a huge open world party based RPG, but with larger parties than most games, and rather than having a set number of characters, you could recruit unique people from almost any race in the game (Which would be quite a bit). In addition, the amount of progression for each individual unit would be very large, with a huge amount of classes which progress in a sort of outwards branching path. For example, suppose you recruit an untrained dwarf. His class would be Rookie. Upon a certain number of level ups, he could become a new class, based on his equipment, and his skills, which would improve with use. So if he was skilled with unarmed, quarterstaffs, or divine magic(which would essentially be a skill for praying), he could become a monk. Then, if he focused more on weapons, he could become a guardian, or if he focused more on divine magic, he would become a cleric. And so on and so forth.
Both races and classes would consist of a mix of more traditional options, such as paladins, dwarves and orcs, and partially or completely new options, such as deeplings, which would be blind relatives of dwarves who at some point became shunned the surface and became physically frail, or maybe a class such as a crusader, which would be similar to a paladin, but the benefits from divine magic is more offensively focused.