First person to make a VR game like this will get my money;

>Multiplayer
>Whole game is in a car/van/truck/minibus depending on how many are playing
>One player drives
>One player sits in passenger seat
>Other players sit in back/other seats
>Internet radio
>Open voice comms
>Procedurally generated roads/highways/traffic/weather
>Can opt to just drive for freeform fun or have it generate you a destination, wherein the passenger seat player has a map and can give directions
>Players in other seats get to focus on chat, scenery, can come up with games to play

Ultra secret stretch goal tier:
>[spoiler]More than one group of players, multiple vehicles of people with mobile phone/CB radio comms[/spoiler]

Just a social travel game, all about the journey.