I suggest to allow Trap the Soul to work on red/purple named under certain conditions - such as being under 1000 HP - to allow players to get soul gems of various raid bosses for super duper cool cannith crafting recipes.
I think that this would be a great way to add new depth to raids. Turns out that it isn't good enough to actually kill the boss, instead, if you want the crafting mat you have to first get the boss to 1-3% of his HP and then survive long enough for an arcane to land a trap the soul spell.
The recipes could be all sorts of things.
/sign if you like the idea (though feel free to make suggestions on how it could be adjusted).