Currently clothing repair just costs a bit of thread. I was thinking it could also cost some of whatever the material. So repairing cotton could cost rags. Also allow repairing of leather goods using leather pieces. Maybe even add in a bit more advanced for later. Disassemble a plastic bottle for plastic scraps. Perhaps disassemble a kevlar vest for kevlar scraps to repair another vest? I know, repaired a vest like that makes little sense, but oh well. It’d be cool anyway. 
We already have the scrap metal for metal armors. If the armor is made from more then one material you could always randomize it and put it in the item info “A rag is required to repair this item.” Could even have a random chance of not required a rag and just thread (a simple tear).
As of a day or two ago, the dev version does indeed use rags or leather patches for sewing, and it’s possible to repair leather items :).
There’s still more work that could be done, of course, so feel free to keep brainstorming.
Damnit! They beat me to it again! 
Mmm, tasty. Almost tempting enough to make me switch over to the dev build and play around a little.
On the other hand, since the current ‘stable’ version still has big patches of NOTHING scattered around, I’m a little leery about moving up to an ‘unstable’ build. Perhaps some of these new features could go into the bugfixpatch?
Hm… perhaps using chitin to repair clothes? Gives more defense, but increases encumberance?
That’s a case where we don’t really know what’s going wrong, or how to fix it. In general, it seems that the unstable version is mostly as functional as the release version, but there are occasional cases where a nasty bug gets in, and it can take us a little while to fix it.
I was kicking around the idea of repairing damaged chitin gear with a fresh chunk of chitin and a minute or two. Not sure what the devs thought of that.
Chitin-reinforcement adding encumbrance seems not that different from simply having chitin gear. I suppose it could help something like a Cloak/Trenchcoat/Fur X/Raincoat, though.