So you beat up some goblins and they have left corpses, blood, weapons, armor and clothing everywhere. Aside from the blood and clothing everything else is relatively easy to deal with (melt the armor and maybe the weapons, use the acceptable weapons, throw the body on the refuse pile and wait for the bones to appear). Yes you can sell the clothing but it doesn't contribute to fortress wealth, unless you decorate it.
The options as I see them
1. Naked Goblins and Kobolds: remove all clothing tags from the entity entries. No clothes, no problem. Downside is that the siege might freeze to death in cold climates (not such a bad thing but it might steal kills from your dwarves).
2. A reaction to turn clothing into thread (you could do cloth, but cloth has a quality multiplier on it). It would probably look something like
[REAGENT:1:ITEM_ARMOR:NO_SUBTYPE:PLANT:GRASS_TAIL_PIG]
[PRODUCT:100:1:THREAD:PLANT:GRASS_TAIL_PIG]
The downside though is that it will work on any clothing in the stockpile, which would be annoying, especially if it targets a Masterwork (or a triple masterwork, weaving, dyeing and sewing).
3. As #2 but edit the clothing choices for all the races so that the enemy races all wear clothing the normal races don't (ITEM_PANTS_PANTS_EVIL instead of ITEM_PANTS_PANTS) and build the reactions to only target those clothing types.
4. Not possible at this time, but maybe in the future we will be able to target reactions on clothing that is NARROW, SMALL, LARGE, or STOUT.
Am I missing any options? Will that reaction even work? General thoughts on the matter?