I too would like croutch, but the amount of codeing it would take would be immense. They have to create new animations for crossbows, some of the throwing weapons, and in general, all sorts of stuff. While yes, crouching would be a very excelant addition to the game, I don't think that we will be getting it any time soon.
most of the animation is in the lower body, actually the upper body could probably remain untouched in terms of animation. but i definitely see your point, with longer armors like surcoats, the texture would get all stretched out and be messy.
but perhaps there is already a mod for crouching on the taleworlds forums? alot of modules have crouching, maybe there's a public crouch mod that could be tested, and if liked, implemented.