A* adds heuristical minimum possible path cost from added tile to goal, which is not necessarily straight-line cost. More effective A*-based algorithms mostly works with other heuristics.
True, but they typically have a smaller node space(512^2 = 262k nodes is big in pathfinding, DF can be 50*288^2 = ~4.1 mill nodes) and limited connectivity(
mostly just the 4 cardinal directions,
sometimes 6 x-y-z axis directions,
sometimes 8 compass directions, DF has 10 + special cases such as doors, ramps, flying, and swimming).
This has all been discussed back in the thread. The main conclusion of this thread was that the best course was to try and limit the ground pathable space by transforming it into a smaller and quicker to path node space(+95% of pathing is over ground so it makes sense to focus there). Several white papers with different methods were put forward, and some other novel ideas were suggested towards this end. A bit of code was written in the vein of one of the white papers and it was partly integrated with Khazad(there were pictures of paths posted), a few suggestions were put forward for how to make a benchmark for different methods but nothing was really put together.
Really, read the thread, or one of the dozen of other threads. Many things have already been discussed and it is just not an easy problem to solve. Significant concessions and
game shaping choices may need to be made to
really improve the pathfinding.
Knowing one way or the other would require Toady who has indicated he isn't really interested in this, at least currently. This is due to the necessity of waiting on/being pressured by other programmers and schedules which Toady has said repeatedly would steal the joy out of it for him. It is something of a miracle that the graphics code is being revamped like it is. Besides, Toady already feels like he may be looking into pathing related issues(siege improvements, multi-tile creatures, digging enemies, workshop and item hauling) in the "near future."