Actual
one-way paths won't work due to a connectivity optimization on pathfinding: It won't even start the A* algorithm unless the two points are known to be connected. (This is also why the game can seem to pause for a bit when two large areas get connected or disconnected.)
However,
one-way traffic designations could work well, at a memory cost of at least one more bit per tile. (Every tile in the map, or at least in blocks where any tile has a traffic designation.)
That bit gets you four more options for traffic designations: N/S/E/W. To use N as an example, a dwarf heading north into the tile sees a cost equivalent to a High traffic designation, while a dwarf heading south into the tile uses a Restricted cost. (Ideally, NW or NE into the tile would be Normal, E or W would be Low, and SW or SE would be Restricted.) This leads dwarves to use the path in the correct direction where possible, but still lets them go the wrong way when no alternative presents itself.
A second extra bit can get you up, down, and diagonal designations, but those are probably less useful, and would slow down the pathfinding algorithm even more.
Whether the slowdown in each pathfinding operation is offset by the reduced need for pathfinding around conflicts remains to be seen. (Personally, I'd like to see that conflict-resolution pathfinding improved, too, but that's an entirely separate issue.)