Worldgen settings would default number of ghosts at 20-25. That would actually mean 20 types of ghosts as with other procedurally generated creatures
Changing the setting to zeo would mean no ghosts, setting it to one would mean that every ghost generated was a forlorn ghost, as the setting increases any deaths that fit the qualifications for a type of ghost, will choose the one with higher priority up to number 11 including the murderous ghost. Over 11 generates ghosts with characteristics the vanilla ghosts and new characteristics allowing them to eat your food stockpiles, or attack a specific enemy that could be invaders. When the settings cranked up ridiculously high a dead creature is more likely to become a procedurally generated ghost.
Making ghosts an interaction would also allow other interactions to disqualify a creature with a single line of code, which might be desired. Does husks becoming ghosts make sense to someone who ghosts make sense?
As for why I think it should be a regional interaction with a default of All regions, is that when something in fantasy is really unbelievable, I like to have an explanation provided. I know that sounds more science fiction than fantasy, but it is done in fantasy, the explanation is just not as technical. Tolkien gave an explanation for his ghosts that was they broke an oath that was sacred, and therefore magical in tolkien's world. They were held not by their own power, but by the powers that be. He also gave explanations for elves, dwarves and goblins as humanoids similar to ourselves, so that people don't realize that wasn't the mythological origin for them.
Creatures rising from the dead as an exotic energy/matter just because they weren't buried and didn't get a memorial just does not make sense to me, unless that same exotic energy/matter is a part of the enviroment and burying them, shields them. If the characteristic that makes a creature become a ghost in fantasy is a part of them before death then it should be just as apparent and effective before death if not more so.
If they can see as ghosts, then they should see fine without eyes, the same goes for other sense organs, as well as the vocal chords should be uneccesary if they can talk as a ghost. If they can move as a ghost, they shouldn't need muscles and nerves when alive, and if they can remember they have some sort of attachment to their body they shouldn't have memory problems with their brain damaged or removed. That they can only do without these things when the physical processes that support life fail them is ridiculous.