I would really like it if we could get thralls that would repair damage inside of buildings. This could work in conjunction with a repair supplies station like the one you use to feed thralls. That way you would still need to fill it with repair materials so its not free.
Running around with a repair hammer and trying to get to out of the way spots is a pain, and this could fix it.
They would not stop decay, just keep buildings and such from losing strength over time, and would be great to avoid seeing repair icons all over the place when you use a hammer.