I think it could work as kind of a mix between Adventure Mode and Fortress Mode:
1. You move the wagon and dwarves around by (T)raveling on the world map. Perhaps before embarking, you could mark possible settlement areas on the maps available to your civ, which would then show up as "quest" waypoints on the world map.
2. You drop back into "regular gameplay" (not the travel map) if you get ambushed, or if you need to scout the area or forage for provisions. You could set up a temporary camp along the way, including mines and workshops. Deconstructing the wagon would turn a temporary camp into your real settlement, but as long as you have a wagon, you can still pack up and travel again. This would require a trade-depot-style interface for getting stuff back into the wagon.
3. Even if you haven't started your fortress yet, any "regular gameplay" (as above, not on the travel map) should take place in real-time, just like Fortress Mode. Turn-based is kind of pointless when you're not directly controlling anyone. You'd still be able to pause, of course. The Adv. Mode LOS stuff probably isn't practical either.
So you could leave the mountainhomes and be happily moving along the travel map until you take a detour through The Foulness of Glooms and get ambushed by a pack of zombie wolves. Back into regular gameplay -- your wagon is in the center of the screen with the dwarves clustered around it, and ringing them are the wolves. The game starts auto-paused. The axedwarf (whom you wisely chose to bring along) fights off the wolves, but not before the farmer gets a chunk of his leg torn away. Should you set up a temporary camp in the evil forest so the farmer can heal, or should you press grimly on toward death and glory? THE CHOICE IS YOURS!
Yeah, this could go places.