He's a maths Ph.D. not a Computer Science or IT Bs.
I think that, had DF been programmed in a language that was more maths friendly, and less "write it like algebra on paper and let the compiler do magic" C then it might drastically increase the code efficiency. But the times he's been offered help with someone else writing a UI, he grasps that the UI needs a stable game API to make calls to, or a means to pass messages, and the game is not in that state nor is he going to re-do the UI each major version to keep it up to date. The same applies to pathing, it's not his field of maths (go read his thesis, it's very far from code related). A threaded pathfinding library has been offered to him, but since the objects change and the map representation changes, he presented some past problems that libraries couldn't cope with and the coders reading the discussion (myself included) wanted to launch kitten and whale rail guns.
Hell, tiles of his maps already store so much data, that it would make almost as much sense to use a memory intense pathfinding and allow each tile to determine the closest (gem/food/water/workshop of each type/etc) than to have each dward parse the map tree each turn to avoid running into each other.