I'd had an idea about this as well.
Part of the idea of the gameplay seems to be a connection between all the stuff you're doing on your own... all the sidescrolling and item hunting and whatnot... and the stuff going on in the settlements. It IS basically the whole idea of the game, after all.... you're trying to work towards improving these places as much as possible and helping people survive.
Well, right now there's a major disconnection between the settlement stuff, and the overworld map when you're in explore mode. Run around all you like, there's nothing resembling a connection until you're actually down into a dungeon of some sort searching for things to help you improve the world.
So my idea is: Perhaps, for every so many tiles you move, let's say, er, 30, one turn passes on the strategic/settlement level. This would change ALOT of things. It would make distance matter, for instance; finding good, convenient routes on the world map or exploring for shortcuts or something would suddenly come into play, whereas right NOW, the actual layout just doesnt seem to matter at all. Different tile types, or even level numbers, could modify how fast/slow your guy travels through/past them, altering how long it takes to get to the next turn change. Thick forests, for example, would make sense to take "longer" to cross than, say, open fields.
And this all just makes sense in a logical way as well; right now it seems a little funky that you can go explore the world outside, go into silly numbers of dungeons, run all over the world, and when you get back to the settlement.... absolutely no time has passed and nothing has happened simply because you did not click the magic button that allows it. That part has seemed very strange indeed to me since the start. It just feels off.
That's not to say that you wouldnt still have the end-turn button in the strategic/settlement modes, but it would make exploring the worldmap much more.... er.... dynamic? I"m not sure if that's the right word. But it'd add another layer of strategy and challenge to the one section of the game that, right now, seems absolutely devoid of it.