Oddly enough, I didn't see much about it on the big dev page.
I think it would be interesting if Thoughts had a little more complexity. In general, I don't have a problem with the system of taking all active thoughts and adding their values. But I had a few ideas for tweaking it.
First, variable duration...
* Losing a loved one lasts for a long time (a week for a pet, a few years for a spouse).
* Sustaining injury lasts for the period of injury, and the severity depends on the severity of the injury. Minor conditions (hunger/thirst) tend to go away as soon as the condition itself does.
* Witnessing death lasts a week or two, the first time, but the dwarf becomes permanently desensitized, both in duration and magnitude, as they see more death.
* Failure to have mandates/demands met is as arbitrary as the demands themselves. Some nobles will obsess about it for weeks, some will have forgotten they even passed a mandate by the time the deadline expires.
* Major accomplishments (relationship changes, noble ranks, artifacts) will also have long-lasting Thoughts.
Most of the remaining thoughts go into a big category called Quality of Life (including admiring and disgust, chatting with loved ones, being consoled, caretaking, being in jail, etc.). Most of these thoughts have a duration of a day or so, though they can be triggered again as soon as they expire. Every dwarf has an expectation of QoL, and happiness/unhappiness is relative to this. A dwarf who expects to sleep on rocks will be ecstatic to sleep in soft dirt. A dwarf used to a finely crafted bed will be unhappy in the same situation.
Having positive QoL tends to raise expectations, and having negative QoL lowers them, so dwarves tend to become inured to any static situation -- however, there is a minimum level of expectations, and it's higher for legendaries and tends to ratchet up with noble rank. Personality traits play a role in this process. Moreover, and also very much depending on personality traits, dwarves will weigh their own expectations against the average expectations of their fortress. If every dwarf has a meager bedroom, everyone is fine. Once half the dwarves have nice ones, the have-nots will be more prone to unhappiness.
It's a few more variables per dwarf (QoL expectation, number of deaths witnessed, etc), but not a ludicrous amount of additional bookkeeping. Thoughts?