While the above are some ideas, which I think someone complained about already, now I'm going to introduce something new, which I'm going to call "Poo-System". Yes, You're eyes work fine and it's indeed "poo" I'm going to talk about.
The poor hearthlings and animals don't ever go to the bathroom and this could lead to serious belly problems, like constipation.
First of all, let me explain the animal "Poo-System". Every once in a while, like once an ingame-day, or more, there's a probability that a certain animal will poo, with no distinction between races, and this poo will decay in one real time day. This poo can be collected, like some piece of soil, and can be placed in barrels. The poo quality will be the same as the animal that produced it and softcaped by the farming skill or survival. After a week in the barrel the poo will turn in "solid poo".
Now, you can take the solid poo and some kind of stone (and perhaps bones too?) to the quern (or a new tool) to make them powder and have as the final result: fertilizer! Softcaped by something like will, dexterity, lore and farming and with quality based on the products used. The fertilizer can be used on the fields and it can increase the probability to have a higher rise in quality and a decreasing prob. to lower the quality of the harvest. The higher quality of the fertilizer the higher will be probability on the harvest grow in quality.
To avoid the over usage, which could bring an exponential rise in quality, the fertilizer could be used once every three to five harvest on the same seed and naturally you can't have a rise in quality if your farming skill is below the quality of the seed.
Secondly, the hearthling poo. I don't think it should be used as fertilizer but it would be cool to have a hearthling making some strange noises while in this kind of WC:https://i.pinimg.com/736x/70/56/7c/70567c39b23a8974a0d0d5f17b0ed5f9.jpg.
The hearthling could go to the toilet at maximum once per ingame-day or more and after the deed the FEP value given by food will have a temporary increase in value.
This are my 2 carrots of ideas. Are they worth something or not?