As much as they can, and not limited to public recreational activities like bar games and bowling, but to add also as many new establishments to visit as possible. Do whatever it takes, including walking into a door and loading somewhere else in interior land again - we won't mind. Let us go to all these places on the ingame internet before we even think to seek out their site ingame.
Make the whole damned game random encounters and tasks and activities, live in the game world meet people like IV and V let you do, but on a much larger scale, both in amount and interaction with each, even if it means scaling back the main story or staggering its availability to artificially lengthen it. Makes it more sandboxy.
Just don't icon spam. This should be discovery based. Driving discovery content and stuff. Sellin that puppy. Just make it awesome again. V really is watered down, as fun as it was, it does not feel like what should have come after IV came after SA.