my tl;dr interpretation of OP:
"I would like these features included with night creatures.
1. Becoming a night creature, probably due to a night creature injuring you, or the hag-kidnapping example Toady has given.
2. Night creatures being vulnerable or immune to different weapons and materials.
3. Night creatures getting together and forming packs and communities, and being able to hunt an entire community for a quest.
4. Variety, different night creatures, etc."
"With the new stuff being put into adventure mode soon mostly the night creatures, I was thinking for both adventure mode and dwarf fortress mode you/your dwarfs could be cursed when trying to kill these creatures...
So say, like, in Dwarf Fortress mode your squad kills a werewolf, but your captain is heavily wounded. He has a 20% chance of being infected with Lycanthropy, and then you would have to cage him or kill him because every night he would become a werewolf....
And then in Adventure Mode this would work out to where you had a certain percentage of becoming the creatures you are trying to kill if you get injured by it.
I think it would be cool, being a werewolf in the normal unmodded DF, and then you could put in more features to make it more exciting. In the update bit you had a post on Dusk Trolls and how hags created them... If you sleep in the wild or in a town with a hag nearby you have a chance of being kidnapped by her (the chance is higher if you're more famous) and being turned into a troll.
The hag would then give you quests as you slowly become more of a troll... and if you did not want to be a night creature then there would be quests to get rid of the curse..
In some cases, some weapons will only hurt the night creature while other will kill it outright, so if you did plan to attack the you would have to search around for info about what hurts these night creatures ect ect...
Collections of night creatures would be good as well, for example, if you became a werewolf you could find a pack and join it and get quests from the alpha werewolf and try and work your way up the pack ladder, or for vampire you could find covens of them and stuff like that, and if you were a night creature slayer you could get quests to kill whole communities of night creatures. Basically, night creatures should have some sort of society entity like other races do.
I also hope to see the variety of night creatures expanded in the future to accommodate many different myths and legends."
[sections redacted for redundance]
I'd say, if I had to guess, that it's pretty likely stuff like that will be added in the future. And when Night Creatures are finished, modding in new ones will likely be like modding creatures now, except with some more fun tags to work with.
But first he has to get night creatures implemented, working, released, evaluated and the inevitable bugfix release or two
P.S. I wouldn't have taken the time to edit the OP and hash out it's meaning if I didn't think they were good ideas myself, and I also don't see too many night creature suggestion threads.