I'd be really interested to see an action RPG type game that just embraces the real-life scale of the world and lets you screw about with the rate of time passing like in Kerbal Space Program when you're walking a long way. You'd have to limit the scale of the story to make it manageable to develop, but I think there's the potential for something cool in there. Maybe there are only two or three villages in one valley, but they're all full villages and they're actually several kilometres apart. Make sure that whatever goals you have are time-gated in some way so that you actually have to weigh up whether you can afford to walk to the other village, because even though you fast-forward it so that it only takes a minute of real-life time to walk there it's actually most of the day in-game.