Although, what would be awesome (more than the above suggestion), would be slave working animations. Although they would have to stop working if the player character choses to free them.
This is exactly my intention for one cell in a WIP mod.
Probably, a long loop solution is the best suitable in this case.
I have made digging animation. I it is not perfect but works and could be fine for background NPCs. I can upload the nifs in case anybody is interested to test/help. IMHO it is better to find a general working solution and that to apply it for other similar animations (videos, pictures are fine but in-game tests are final and more informative).
However, we are facing another problem: how to "give" tools to NPCs?
These tools could be:
1. Lights that can be carried (not working in day time for me),
2. Weapons (not working with idles, even with "equip" function call).
3. Clothes/armor (not very elegant solution that requires serious scripting for an "active" NPC like slaves that should be freed and might not work with two-hand tools).
4. Shield. Two variants: 1. change the pivot point of the tool mesh/nif in order to fit the shield bone that is attached to the left arm (not working for me so far, I have made only few attempts in NifScope); 2. Rename the "weapon" bone to "shield" and "shield" bone to "weapon" in xAnim.nif animation file (skeleton structure). "Shield" bone should be animated in the case of two-hand tools. This works, but NPC becomes left handed and does not correctly use real weapons. However, for unarmed NPC slaves this can be fine.
5. Body part (that will be really very strange new race).
OK, granny with a broom is left-handed, but smith is right-handed. What are your solutions? Broom is, perhaps, a shield, and what is smith's hammer?