Ability to sit.

[Acolyte]

I mean, you have benches, right? 

This also may be a usable alternative to standing for some tasks if there's also a table nearby. Handy when you want to tan that bear skin you worked so hard for - so hard you can't stand due to leg injury....   

   - Shane

[JEB Davis]

I've thought of this many times too, although not sure what priority it should have in development.
You could sit while fishing and in your punt also.

[PALU]

While there are many occasions where you'd normally sit, I don't think it adds to the game (except tedium) to explicitly model sitting down/standing up.
Acolyte's suggestion that a table + bench could substitute for the required ability to stand for some tasks makes sense. I don't know how much effort it would be to code it in, though, so I don't know if it would be worth it.

[Acolyte]

The way I see it, it could work like wading/swimming. When you enter a wading hex, you wade, in deeper water, you swim. No input needed if you have the toggle set for that.

I'd see sitting the same way. you put you character on a bench and they sit.

As for modeling, you'd need 4 sitting positions. Knees up to the right/left and knees down to the right/left. Modeling this would not be hard, adding them to the tile sheet may be an issue if it has limits on size.

For programming, it's a new stance. This might be the tricky one, I don't know how much would be involved there.

All in all, it's a little thing - nice visually and handy on occasion. If there's a choice to be made (timewise) I'd rather have Textilecraft and Tailoring skills added, but these are already on the development list and sitting was not - and this is the place for suggestions, is it not? 
   - Shane

Edit: I'm an idiot - you'd only need two - facing left and facing right. Knees up when facing left, knees down for right. Your character looks left for SW, W, NW and N while looking right for NE, E, SE and S.

Be better if the furniture got turned 90 degrees, though. The way you sleep on a bed looks downright bad for your back.