I am suggesting Smart Doors - instead of locking them so no pets or no Dwarfs may use them I am thinking that maybe making doors that can allow or prohibit certain Dwarfs, either by name or maybe even jobs. For example only allowing Miners, or certain Miners, into a mining region. I would suggest this for two reasons -
1. While I find barrows useful for a Red Alert kind of command, pulling everybody but the military into the Fortress's lower levels I would like to have some detailed control over traffic within the Fortress. I don't mind my medical staff hauling stones in the living levels if it helps in building proper walls, floors, and roofs. But I don't want them working in the deep, dark, a 100 levels down, mines. Hauling gives them something to do - but I want their jobs to be short and I want them near the medical centers. In order for barrows to work you have to adjust them as the Fortress grows which could be a tad confusing if you have overlapping ones. With smart doors you would just have to slam in a few more or remove them on the needs of the Fortress, or edit those that you already have.
2. Many players are starting to think about eugenics, breeding, and the whole 'Time Machine' split idea - making one race into two - and the use of doors to help split or at less decrease the chances of certain types of Dwarfs marrying would allow for more control over such 'projects' of Dwarf !!SCIENCE!!.
For example, allowing them to share the same stockpiles but using doors on the edge of the storage chambers to make sure they don't enter the other groups' living areas, dining areas, and work spaces would help greatly without having to mess with tracks, barrows, and pits. We could, in fact, design areas for the breeding of miners, surface workers, nobles, and so on. Making not just a class system with a slum area but a caste* system such as ants have.
Let us say your miners, or underground workers, enter from the west doors. You can make it so only THEY can use that door. And the east doors is used only by those coming from the surface or sub-surface society. So they would not socialize with each other, share bedrooms, or even idle. They would just run into each other during their work hours. Of course, this would require more than one functioning Meeting Hall - I assume that would not be a problem. They would both have access to the stone, wood, finished products, food, animal products, but have their own workshops (depending on their skills), so on.
Even without a advanced DNA system those underground and those near/on the surface would develop certain traits - like how they react to the sun.
Children could be assigned to certain bedrooms in certain regions depending on their stats, and the wishes of the player. Once they become an adult their skills could be adjusted to fit the society they will now live in. What a Brave New world!
* Not sure if they has a 'e' or not.