A heating system could use straw for burning, of course, wood is better but where else put the straw.
Would love to see a furnace for great hall or personal quarter heating and decoration!
This would be neat. Especially in winter. If there were an ambient temperature based on the season and it affected the mood of the gnomes. With more personality programmed in it could get interesting, but an obvious effect is them being less productive, needing sleep more, being hungrier to cope with their bodies needing to work harder to stay warm (which is really bad in winter). If they then had different clothes through the dressers, they could stay warm or cooler in the seasons, dressers could be stocked with summer and winter clothes. The extra heat of summer having a similar effect but requiring them to need to drink more.
Clothes could also be used like in DF to represent status and perhaps some sort of effect on their social needs, perhaps as part of their personalities they have some sims like features, they need to talk to someone occasionally, they have friendships and get major bonuses from talking to their friends (maybe this can lead to families?) or their mood goes down; also if a close friend dies they may become very depressed for a period. They also have various interests that are productive but not necessarily for the sake of production. For instance some gnomes are more fashionable, they make various hats, colored garmets, etc. They would be happiest wearing their favorite clothes. They may also be crafty, so they make puzzleboxes, but for their room or something? Maybe they give them as gifts. Since they were made for them they hold a special value that grants a mood bonus. Because they are more satisfied they have better moods (perhaps moods affect others and are socially contagious, excitement, euphoria, contentment, as well as anger, depression, insanity etc.), combat bonuses (like being energized, confident, aware, focused, as well as afraid, distracted, etc.) This would alter the circumstances of combat based on leadership, the quality of food and rest the soldiers get, as well as their own social needs. Mood would alter your industry based on how well managed you were. If you can't keep your gnomes happy they will slowly head toward depression, infighting, and insanity.
One last idea for gnome specific states or whatever, is sickness and health. Maybe they can get the sniffles from being out in the rain too long without proper clothes? Rain jackets need to be made from cured hide? Perhaps various underground monsters have diseases which can spread if they aren't contained and treated?
Maybe this is too complicated. I think it'd be funny if occasionally a gnome thought they were a prophet and began a religion.