I always found it underwhelming with only 4 kinds of madness in the game. I also find it underwhelming that mad dwarves die pretty fast - I'd find it neater if a dwarf could live a long and weird life while being mad.
Ages ago I found a game that had a mechanic that could be usefull - phobias. It was just, whenever a madness-inducing thing occured, you'd roll a d100 on a table of a ton of phobias and you'd get a new one.
It resulted som fun emergent gameplay - I think also in DF it could create some really unpredictable situations.
I think a phobia should be gotten like if a dwarf is #under a lot of pressure# and uo then has a an intense negative emotion. Then they dwarf would get a random phobia from a long list of phobias. It should be possible that it went away, maybe in the opposite condition than getting them (great mood and intense positive emotion)
The list can be made with the relevant one from say
https://en.wikipedia.org/wiki/List_of_phobias or any book with a nice list of phobias.
In DF Bibliophobia (books) or Equinophobia (horses), Emetophobia (vomiting) or Gephyrophobia (bridges) could result in some interesting situations.
I think a phobic character would just run away from the phobic trigger if they saw one. So if a bibliophobic dwarf comes across a book, he'd just instantly run away and hide for a while somewhere, then he'd calm down and be normal again. So in many situations it wouldn't matter, an it would just be this little thing that made a dwarf stand out because he's crazy.
Wouldn't it be fun if a scholar got bibliophobia? Or if this one dwarf just couldn't cross bridges?