If I had known earlier, I'd have already been working on it. I might yet, I'm going to take some time tonight to decide.
This is my concept right now.
Taking the three themes "City", "Edge", and "Desert".
I need to think of a resource. Or three. Anyways, there's this desert. With cities all around it. You'd think they'd just leave well enough alone, but no, there's things in the desert they need. Badly.
So they fight over it. not with armies, no army could cross the desert. They send proxies into the desert to claim and retrieve these necessary resources. The good ones are called Wastewalkers. The ones in training are called Journeymen. They are the rough men in the saloon you don't want to cross. I haven't decided yet if they're wearing long dusters and revolvers, or boiled leather and longswords. The period hasn't been ironed out yet.
The party would probably be a group of Journeymen. They can work for any number of cities. They just want to be sure their clients don't start finding out they they're working both sides. They make their coin by bringing back what's needed, and any extra salvage they manage to find. An encumbrance system is going to be vital, to keep the setting feeling nice and gritty.
For inspiration, think Fallout, Book of Eli, The Road. Only based around a central, resource-laden desert that serves as the central point of conflict.
If I start this project, I'll need to rewrite my GRIT mechanic, incorporate an encumbrance system, decide what resources the desert holds, why the surrounding cities fight over it, make some form of map (I'm garbage at digital art), and have a decent beastiary. The beastiary is going to partially depend on the setting - a medieval desert wandering game will have a different assortment than a post-apocalyptic desert wandering game.