I envision a world embark.
You still pick your little slice of territory as 'your area', under your direct control, but the map is no longer limited to your embark. It stretches the entire world. Unmapped terrain and Fog of war exists beyond your borders. Dwarfs sent out will uncover the lay of the land and push back the fog where they are at, much as adventurers do.
As for your fort, it may extend as far as you want in any direction you please. Want to build a road to the mountain home? Go for it! A huge bridge connecting an island with the mainland? Make it ostentatious, with golden pillars and platinum railings! Want magma but don't want to dig down and pump it up? Build an aqueduct to the nearest volcano and bring it here! Establish mini forts days away from your main fort where your dwarfs can operate from for work or patrol duty! Tired of zombies? Besiege the tower yourself with your military! Disassemble the building brick by brick or collapse it with a support/lever.
People and creatures will wander the map in real-time. Caravans no longer come at set times, but however long it takes to get to your fort and back to where they came from. Animals no longer come in groups onto the map, replaced quickly after leaving an embark, but are free to wander into and out of your embark as they please. Sieges will have to march to your fort to attack you (much as they do now) but you could scout the terrain, determine (or 'arrange') their best path to your fort, and build a guard house their to alert you of impending invasion!
So many possibilities.