We we should go ghost busters, rather then wait for a bug fix?
I think one of the selling points of DF is that it doesn't feel like a cliché game, but rather has a nice little unique flavour, even for the genera. It we suddenly break out the 'Holy sword of +5 ghost slaying' then we are just using a over used gimmick.
I don't think that people are asking for that.
But. Look at my sig. It's all right for Dwarf Fortress to represent fantasy cliches! Much of the meaning of the game comes from the way it builds on existing myths and legends. That's why it's Dwarf Fortress rather than Smrgoph Fortress -- drawing on existing myths and legends lets players relate to it more easily.
Various ways of banishing ghosts appear in a lot of myths and legends; they can make interesting stories, and should be represented by the game. These include satisfying whatever regrets tie the ghost to the world; religious or magical exorcism ceremonies; destroying some object that ties the ghost to the world; or, yes, using a holy relic to destroy it.
However, Dwarf Fortress puts those things in an interesting or vibrant universe. What if it isn't a 'holy sword of +5 ghost slaying', but the legendary relic of an ancient god's prophet, which had the god's blood fall on it when he died, which was later used to slay a monstrous lord of the undead, with a long line of legendary heroes who've wielded it? Something like that ought to do something to a ghost (possibly!)
Don't discard ideas because they're overused. The ideas that are used a lot are, often, the ideas with the most mythic and thematic resonance -- they're
good ideas, even if they haven't always had the best implementation. Try and think of ways to make them more interesting instead!