So... I mentioned this on the update list but thought I should move it over here. I am utterly projecting here, and what I am thinking is probably not going to be possible for a while, and depends upon Toady's updates being just like I hope they will be, which is no guarantee but...
The addition of souls in-game could be especially awesome if souls become droppable items, that can be used to possess items, or to inbue items with certain powers.
The addition of favoured weapons for dwarves (an perhaps weapons being given names if they are favoured and used in a legendary battle) also opens up exciting possibilities.
I read someone suggesting that named weapons should gain some epic qualities, or special attributes, or gaining artifact status, and there was some discussion as to how to implement this. If souls are going to be created as droppable, useable items, this could be a great way to work in the whole thing with named, artifact weapons.
For example...
Big McLargeHuge (I rename all my champions after that MST3K episode), Champion and hammer-wielder, has a favourite hammer. Big gets involved in a large-scale siege on his fortress, and defends the fortress well, taking out a massive number of Goblins. The weapon is also used by him at some point to defeat a Titan, or a Hydra, or something. After injury and coalescence, you decide that Big McLargeHuge deserves some sort of reward for his efforts. At present, the only usual choices are to build said dwarf an epic burialchamber, or give him his own extra-awesome bedroom or something. But what if you could gift him with a legendary weapon?
Now, Big has a favourite hammer. So you assign the hammer to be possessed or imbued with the souls from some of Big's own fallen enemies (collected after the battle, 'natch), and engrave/decorate the hammer or something while you are at it. As a result of this, the hammer gains a name, and gains artifact status. It may also gain additional useful properties based on the possessing soul (like, say, a sword could get a flaming blade if imbued with a fire dragon soul, or a shield imbued with the same soul could be fire resistant).
Alternatively, if the dwarf in question has a really shitty weapon he treats as a favourite, you could maybe perform this possession on a specially-made epic weapon and assign the weapon to the dwarf?
It would also add some lovely flavour to the item descriptions.
"This is the legendary iron hammer 'BloodMaw GoblinMasher', it is the favoured hammer of the Champion Big McLargeHuge. All craftdwarfmanship is of the highest quality. It is studded with rubies, menaces with spikes of goblin bone and is encircled with bands of dragon leather. On the hammer is an engraving of a dragon. The dragon is screaming. The hammer is possessed by the soul of the Goblin Lanky McIsuckatnames, who was slain in the battle of Boatmurdered by the Champion Big McLargeHuge in the year 315. The hammer is rumoured to drip with the blood of the slain if it is not used for more than a year."
The rumoured part could be a randomly generated thing, like the likes and dislikes of dwarves, and it could be a property given for items such as this where the possessing soul does not imbue any special powers or properties.
I don't know how practical that would be to implement, but it has potential?