There seem to be a number of things sitting around waiting for a pathfinding rewrite. Most notably flyer/swimmer pathfinding being sort of crazy, but with the upcoming new release there is climbing and jumping, and on the horizon there is potential digging and construction. Gonna be one hell of a rewrite once it comes, which by the sounds of things will most likely be along with "improved sieges", since that's the one item that simply doesn't work at all until the pathfinding is working (at least not as it's been described).
Though when that might be is completely unknown
It's going to be interesting to see how all that eventually works it's way to fort mode. I can imagine strange bugs with dwarves scaling cavern walls and swimming through underground lakes to fetch wads of silk on the cave floor and all kinds of craziness. What's going to be hard is representing these abilities without having them used all the time. Maybe someone would scramble over a wall if faced with an imminent threat, but it's much less likely for anyone but some kind of parkour gymnastics ninja to do so while carrying a baby and a load of lumber. There are many strange cases that need considering. Stuff to look forward to though.