As a two-time visitor to Tokyo/Japan there are some things I would really like the developers to include:
Japanese taxis (Toyota Crown, Nissan Cedric), even if many of them were replaced by the more standardized JPN Taxi model, which should also be included. Of course, a taxi mission story is a must.
Also, mini delivery trucks, and delivery missions with proper parking/unloading/delivery maneuvers would be nice.
An out of car walking mode so we can visit many of the iconic locations on foot.
More fashionable clothes and more body types for our avatar. The middle aged and elderly should be included.
A proper international airport and not the sorry strips (sorry my Mexico, but that airfield is probably used only by cartels!) we have been getting. Since Tokyo will be featured, then Haneda should be included.
If we get a big mansion to buy in/around Tokyo, it should feature a multiple-car garage, like PGR used to.
Ravens, lots of ravens. I heard they were trying to curb their populations, but the last time I went the crowing at dusk was unbelievable.
A collaboration with either Sega (Sega Rally) or Namco (Ridge Racer) for the "fun" expansion, with maybe even an optional retro graphics mode.
Those are from the top of my mind. What about yours?