The last paragraph above is the core feature suggestion. Everything else is to make it fit into what i see as the game's directionTrade routes and redundant travel. I love how the game is a continuous set of states that all have physical significance inside the world. There are only a few things that are exceptions: gold, research, but most importantly movement is not one. I really like this decision and find it part of why exploring the world feels like a journey. At the same time, it can be the very reasonable explanation for why back trekking through the world can be real monotonous when you've reached safe lands for the umpteenth time
I bundled trade routes with this topic because it's, to me, the same question just asked to NPC's. I also thought that the two questions might solve each other's problems by interacting. I don't think that trade routes bringing the shop to your door is solving the core issue of redundant travel. Redundant travel just for trade, yeah, but not in general
If the player could interact with the different trade caravans coming in and out of a city hub, as a simple traveller or hired merc, in it for the destination or the gold, then I think the trade route system would over-compensate for back-trekking. This is getting into feature suggestion territory, more in another thread...
Right now one of my favorite parts of the game is the ground breaking feeling that comes with journeying into new territory. Maybe sometimes, in friendly lands, it will be a good feeling to caravan into the comfortable heart of somewhere new first. Get squared in the city and journey out cautiously from there. But it would deflate too much tension and mystery from an expedition into alien mists or into the lands far past slaver territory, unseen for generations
I think a good approach to this would be to make trade routes have factions and respond to faction hostility (to other NPC's and the player). Certain factions just wouldn't take routes through high threat places. What a nice sounding idea, but man, it'd spiral out of scope quick. You'd at least want to be able to compute trade routes based on travel distance, weighted and bounded by geographic faction threat. Then everyone would expect that, when you finally cast down the slaver stronghold, and the regional threats change, some new trade routes might open/change for the opposing factions. And you'd of course want slaver "trade" routes, where they cart people off to market in harsh lands where slaves die without notice. Another big one people would expect is that their city could properly become a hub for trade routes.
Obviously starting to get a bit carried away, but the point is: holy shit, redundant travel could be so cool!